With developer Valve having a fairly hands-off approach to the CS:GO esports scene that means there are a lot of different tournaments from many organisers around the world, all of which work slightly differently. However, there are a lot of core rules and styles that all tournaments feature.
The T side will have to try and plant a bomb at one of two bombsites on the map, the CTs will try and stop them by killing them, or defusing the bomb after it has been planted.
A team wins a round by either killing all of the opposing side, or completing their objective of planting and detonating the bomb (T side) , or stopping the bomb exploding (CT side).
Each map is a best of 30 rounds, so the first team to win 16 rounds wins, and teams swap sides at the start of round 16. If the scores are tied at 15-15 overtime starts, which in most tournaments is a best of six following the same rules if scores are tied again another round of overtime starts until there is a clear winner.
Some tournaments feature a round-robin group stage where teams will play a best of one, or a best of two and can tie, however, most feature best of threes and best of fives, meaning a team will have to win 16 rounds in two or three games to win the match.
Tournaments typically feature a single-elimination bracket, where a loss will knock you out of the tournament.
A lot of tournaments feature open qualifiers that are played online and allow any team to enter the competition, giving unknown teams and amateurs the chance to qualify for the biggest events in the world.