Sit-and-Goes are miniature tournaments which go off as soon as the set amount of people required for the tourney is filled.  They are constantly available for players to take part in, and are usually kept in a different browser section of the online app than the regular tournaments.  They range both in the number of people that are required to fill them up, and the entry fee.  The smaller priced sit-and-goes usually fill up a lot faster than the bigger ones.  They can range in price from a few dollars to 250$ for the entry fee.  The variety and convenience of these tournaments make them a favorite for many players. I happen to enjoy playing them as well.  Heads-Up sit-and-goes are also offered at most sites online, and they provide an excellent opportunity to gain experience with heads-up action while being able to limit your risk to as little 5$ or so. 

Finally, Freeroll tournaments are those which are run either by the house, or by a private party, which cost you nothing to enter.  Private party Freerolls are password protected.  Its just for people's friends.  Freerolls which are run by the house, usually pay such miniscule amounts that its not really worth your time to play, unless your broke and just can't find anything else to do.  In order to qualify for a Freeroll that is run by the house, you usually have to have a small amount of time logged into the real money games. 

As a novice player, small inexpensive tournaments are an excellent way to break into real money play.  For a total risk of 12$ you might get three hours of play time.  Also, even though the entry fee isn't very high, people are usually still playing to win in tournaments, so you don't have to deal with a lot of horrible loose play.  Therefore even lower cost tournaments can provide a valid atmosphere for improving your skills.

The ideal tournament for a novice would be a guaranteed with an entry fee that is relatively low compared to its guaranteed prize amount.  These types of guarantees will attract more players, and therefore have a longer course of play.  The risk is also lower.  It is important to become practiced in playing tournaments with more than 250 entrants.  There are a couple of reasons for this.  First of all, the really high stakes tournaments, (the kind that you want to train yourself to someday win) almost always go over 250 players.  Secondly there are distinct differences in the structure of the play that 250+ player tournaments assume compared to much smaller tournaments.  In order to win you must learn to form your playing strategies around these differences.

1) Early: The beginning of a tournament to the point where almost 2/3's of the players are knocked out.  In a tournament with 400 players it would take you about an hour and 40 minutes to get through the early phase.  Many players suggest that the strategy you should have for this part of the tournament is to play your regular full ring cash game poker.  I disagree with this.  My own strategy during the first hour of play is to tighten up a lot more than I would under ordinary circumstances in a No Limit cash game.  I throw away anything worse than A,Q from any position.

Its a serious disadvantage to play too many hands too soon, or to play inferior cards from any position when 1) people are knocking each other out by the dozens, and 2) the advantage that you gain by doubling up early in a tournament of that size is completely marginal next to the finality of being knocked out early.  For this reason I play even KK and AA a lot more cautiously than I would in a regular cash game.  I have been knocked out in the first hand in a 100$ entry fee tournament with a pair of Aces for a starting hand.  So its not like a cash game at this point where you are only playing with a small piece of your bankroll at a time.  All-in is truly all-in, and that, plus the fact that an early chip lead rarely translates directly into final table results, puts me on the very tight end of the playing spectrum at this phase of the tournament.  I am looking to double up, or nearly double up during the course of the first hour and a half, but ideally in about three separate hands, in which I move in from a superior position with a superior hand, and take just a piece of someone's stack.  Playing that tight I am usually able to achieve this goal.

2) Early Middle: At this point in the tournament players might be starting to check the tournament lobby to see where the bubble point is set.  The "bubble" is the point just before the first winning place is paid.  If 50 players were to get paid in a tournament, the bubble would place 51. So players are starting to put their eye on the prize and are starting to believe that they actually have a chance to win some money for their efforts. 

The other thing that is happening is that the value of the blinds is growing to the point where it is somewhat valuable.  Blinds increase in value during a tournament at defined intervals, usually every 10 minutes.  A turbo tournament is one in which the value of the blinds might go up every two minutes or every 10 hands.

So the blinds are becoming more valuable but not yet valuable enough to make a big impact in the way people are playing, or in the way that you should play.  Now, depending on how you did during the first hour and a half of play, you have to adjust your playing strategy at this point.  If you did well and hit your 3 profitable moves that you wanted-then for the time being you can continue to play more conservatively.  If you didn't do so well, then it will become necessary at this point to become somewhat more aggressive.  The reason for this is that soon the blinds will become valuable to the point where they will begin to squeeze the shorter stacks.  If you have 1200 chips left, for example, and its soon going to cost 300 chips just to get through the big and small blinds-then you know you will be on your way out at that point.  So if you are short on chips at this point you must make the attempt to pre-empt that situation, or it will soon be too late.

3) Late Middle:  This is where things heat up.  If there are 50 places paid, late middle phase would start around the point where there are 95 players remaining.  The blinds have now become quite valuable and are worth fighting for (stealing) in themselves, apart from any additional chips that might be put into the pot if there is a call or a raise.  This fact has the effect of completely transforming the character of play, and you must now change your own playing strategies as well.

First and foremost it turns into a game where just calling pre-flop is very unwise.  There is almost always a pre-flop raise at this point in the tournament, because players want to steal the blinds unchallenged.  Stealing the blinds becomes a priority for all players except the ones who have really managed to come out ahead in earlier phases of the tournament, the top 5 or 6 monster stacks.

So say you are in P5, and you just call the blind pre-flop with J,Q suited-there is a good 70 to 80% chance that you are going to get raised from a later position.  Now you are in a position where you  have spent a lot of chips on a call, and you are forced to put in more on a hand where there is an excellent chance that you are behind from a pre-flop point of view.  Even if you are not behind in terms of your cards that much, maybe the raise was from P8 with a pair of 6's, you are still out of position with a big investment out in front of you, pressured by a raise from a later position.  The bottom line is in this situation, you don't want to be the guy in P5 with the JQ suited, you want to be the guy in P8 trying to aggressively steal it all with a pair of sixes from a superior position.  You will be forced to fold and the value of your call will be wasted.  You can't afford to do that at this point in the game.

Instead you must choose the hands that you play carefully, and if you decide to play a hand it should be raised pre-flop, not just by making a call to the blind.  If your chip amount is average at this point, you should try to steal the blinds on average once every 10 hands.  If you happen to get a glut of good starting cards at this point in the tournament, it is to your extreme advantage to raise the blind pre-flop with them.

4) Post Bubble: At this point in the game, you are in the money, and all the players left breathe a sigh of relief.  After the bubble has been broken there is usually a short period where people start playing more aggressively because they know that they are going to win the value of their entry fee plus a little bit.

What you should do is never-mind that, and form your playing strategy around where you are chip wise.  If you have done well and are ahead of most people, you can play a more conservative amount of hands.  If you are behind, again the blinds continue to raise, so you should play more aggressively.

Keep in mind the tenor of the game of the game has not changed since the last phase-it is still very much a raise pre-flop game and will remain so until the end.  Occasionally you will see a flop go off unraised but it will be rare.  To survive you must continue to raise pre-flop with your best hands and make the attempt to steal the blinds-the only question at this point is how much you need to do this depending on the size of your stack.  Essentially, that's the basic strategy from here on out.

5)  Final Table: If you've made it to this point, one of the last 9 players, then you should give yourself a pat on the back.  The first thing that you should realize at this point is that there is a big, big difference in the amount of money that places 7, 8, and 9 receive compared to what places 1, 2, and 3 receive.  This fact should absolutely have an effect on the way that you play at the final table.  Just like in the early phase, it becomes to your advantage to play less hands.  Unless you are really being squeezed by the blinds, you should allow other players to take the chances and eliminate themselves.  The big difference between regular cash ring games and tournament games, is that in tournament games you can make profits by doing nothing but folding, and in the case of the final table, big profits.

You shouldn't think of your goal initially at the final table as, "I want to come in 1st place", and then try to take the most aggressive path to that end that you reasonably can.  Instead you should think more along the lines of, "I want to survive until at least 4rth place."  I'm not saying don't take the legitimate opportunities when they come to you-poker involves risk-but I'm saying to take a basically conservative attitude, and let that inform those situations where you are struggling to decide weather or not a hand should be played-let it tilt you to the conservative end.  The underlying circumstances of the final table situation ultimately favors that stance.

That's my 250+ player tournament analysis and strategy guide-it has worked very well for me.  Smaller tournaments have a lot of the same elements involved, but they can't really be defined and separated with that level of distinction.  Ultimately the larger tournaments, the ones worth playing, in which you can make big prize money, are going to fall into the phase patterns which I have described above.