There are three main ways to play in a poker game: sit and go (SNG), tournaments, and cash games. While all three play the same game, the manner in which they are set up is different. These styles apply not only to Texas Holdem, but also to other poker games such as Omaha and Stud.
A cash game is just your standard poker game with blinds that never increase and a player may buy in for whatever he or she would like to A tournament is when players start out with a certain number of chips and the goal is to eventually wind up with all of them. This is the idn poker online type of poker that is often shown on TV because of the enormous payouts if you win. Everyone pays a buy in fee and then is not allowed to cash out at any time; it is a strictly play to win and the goal is to collect all of the chips. This type of game takes a much longer time, often days for the larger tournaments. Since there are usually a lot of people in a tournament, you do not have a great chance of winning that often, but when you do you will likely see a large chunk of the prize pool.This is the type of game that is usually the most popular in the casino as there is no time commitment to it, and you can play for as long or as little as you would like to. The blinds continue to orbit the table no matter how many people are playing and people are free to join in whenever they would like to.
A sit and go is essentially a mini tournament. The registration stays open until a certain number of players join and then play begins. Like a tournament, every player begins with the same number of chips and again the goal is the same: to collect all of the chips in play. Since there is a much smaller number of players playing in a sit and go, it often finishes in an hour or two, so it is not as large of a commitment as a tournament is. An advantage to a sit and go compared to cash in that the buy in is capped so you cannot simply reload if you happen to bust out like at the cash game table.