In a regular poker tournament the buy-in fee and start time is known, it is unknown how many people will sign up before it starts. In a Sit & Go (Sit and Go, Sit n Go, SnG) the buy-in fee and starting number of players is known, the start time is not. Basically, you pay your fee to get a seat, when all of the seats are filled the tournament starts. These types of tournaments are a staple of online card rooms and are less common in casinos. This article will mostly address the online card rooms, where differences are known they will be explained.
$30+3 10 up NLHE
T1000 10-20 12 min.
$30+3 is the buy-in, $30 goes to the pot and $3 goes to the house.
10 up is how many people the tournament will start with. In the case of a multi-table SnG, 'up' indicates how many are seated at a table and another stat will show how many tables need to fill up before it starts.
NLHE indicates the game to be played. In this case, No Limit Hold'em is the game. Other games typically offered are Limit Hold'em, Pot Limit Omaha, Limit Omaha 8/b and 7 Card Stud. Some sites will offer the rest of the options: No Limit Omaha, Limit Omaha, Pot Limit Omaha 8/b, 7 Card Stud 8/b and even more obscure games such as Triple Draw Low or Crazy Pineapple.
T1000 is the starting amount of chips for each player. The T stands for tournament. This is a tradition ported over from casinos wherein poker chips are distinguished as being worth cash or only being valuable in a tournament. This prevents someone from trying to cash in a "$100" chip they got from a tournament.
10-20 indicates the starting value of the blinds. To be more specific they are T10 and T20.
12 min. is the length of time spent at each blind level. Some online card rooms use the number of hands played as opposed to a time limit. Either way, they should have their blind levels posted somewhere on their site.
So, those are the basics - now what do we do with this information?
Buy-in Fee
For the hobby player any buy-in that is both affordable and fun is fine. There are SnGs that start as low as pennies on some sites, they may run as high as thousands of dollars for a buy-in. Consider starting out in the $5+.50s.
For the amateur player it is recommended that they have a bankroll equal to a hundred buy-ins (not including the rake). So for a bankroll of $500, start in the $5+.50s. "Playing within the bank" is something most amateurs are incapable of doing, before an amateur turns pro they will figure it out. The reason the suggested bank roll is so high is that pro players understand swings and they understand comfort level.
Briefly, even pros have bad sessions or bad runs. An otherwise fantastic player can go on a losing streak very easily. The comfort level, or 'comfort at this level', means losing the buy-in will not greatly inconvenience the player, they may play their best game without fear of losing. When players will really miss their buy-in they tend to play too tight, they hurt their game by not playing properly for fear they will lose - naturally, they all too often lose for exactly that reason. Strict adherence to playing within the bank protects a player from trying to make up losses with ever bigger buy-ins ("I'm down $200 this weekend, if I can just win this $50+5 I'll make it all up at once" - this downward spiral claims thousands every day).
Starting Chips and Blind Progression
These are very important considerations that very few amateurs understand completely. Here are two examples from actual sites:
Ultimate Bet Party Poker
Time per 10 min. 10 hands
Start chips 1500 800
Level Blinds Blinds
1 10 20 15 30
2 15 30 30 60
3 20 40 50 100
4 30 60 100 200
5 50 100 150 300
6 75 150 200 400
7 100 200 300 600
8 150 300 400 800
9 200 400 500 1000
10 300 600 600 1200
Given a choice between these two the pro will prefer Ultimate Bet, the amateur won't have a preference because they don't know any better. Higher starting chips and slower blind progression favors the experienced player as it gives them more 'room' to play around in the early levels and gives them more time for their experience to outweigh the luck of the fish.
Low starting chips and/or rapid blind progression means that the pots are going to be worth a significant percentage of each player's stack much quicker. This means they will be making all-in decisions sooner in the game.
In the average SnG on Ultimate Bet a player may fold four entire orbits, forty hands, and they will still have around T1350 or so. By this time they have good reads on the remaining players, more than enough chips to be comfortable at the blind level and more than enough chips to still be threatening to the other players at the table. On Party, on the other hand, sitting the same amount of 'time' will likely see the player sitting at around T115 while the blinds are at 50/100 - not a happy place.
This is not to say that Party should be avoided, on the contrary, it just requires a different strategy and different expectations.
Final Thoughts
SnGs are good training all the way around if they are used properly. They are good training for multi-table tournaments in that they teach a player how to monitor pace as regards blind progression and stack size. They also get a player used to and comfortable with the all-in, something that should be seen less frequently in ring games. By 'proper' SnG play I mean the player is entirely, or nearly entirely, playing SnGs. Playing them as the mood strikes or like a lottery will never lead to mastery. Dedication to one site and one game will improve results much faster.
There are many SnG strategies that are beyond the scope of this introductory article. As I node them I will add links here. As promised: check out poker tournament for a strategy guide of sorts. It is written with the tournament in mind but conceptually they are very similar.
And last, as you are out there looking at what is offered you will notice other types of SnGs including: entry tourns, turbos and Step SnGs. Entry tourns pay entry to another tournament instead of cash. Players use these to win entry to tournaments they could not otherwise afford. Turbos are faster versions of the same SnG described above. Step SnGs are complicated and run for different reasons on different sites. Basically though, winning Step 1 pays an entry to Step 2, players work their way through the Steps to the final Step which pays cash. Similar to entry tourns, this is a way for a player with a smaller bank roll to get into a SnG with a much higher buy-in. | 
