Poker rules are about do's and don'ts for different poker variants. There are rules that relate to the blind structure. There are rules applicable for ante. There are rules that dictate how many raises and re-raises can be made in a betting round. There are rules about call, raise, re-raise, check and bet. There are rules about the betting limits and betting structure. This means, poker is played within the rules and limits of the game.
Poker variants different from each other in the kind of rules applicable for winning, betting structure, pot splits, and other aspects of the game. The numbers of players that can play at a poker table, the table limits for the poker room, are all variable and highly specific for different poker rooms as dictated by the management of the poker room.
There are rule variants applicable for community poker games, draw poker games, mixed poker games, and each of their sub variants.
There are Sit and Go tournaments and Multi Table Tournaments. There are Ring games. The rules for Poker tournament types vary as well. So, before you start playing, you should check in to the rules applicable for the poker variant. It is important for you to master the rules applicable for the tournament structure that you might be playing in.