Checking is one of the main actions you can use in poker. When you check, you pass on the action to the next player without adding anything to the pot.
This play is only available when no other bets are active in the current betting round. If anyone else bets, you can’t check but will instead have to fold, call, or raise.
For example, let’s say you are sitting in the BB and call a raise from the BTN before the flop. You will be the first player to act after the flop comes, so you have the option to check or bet, and in this scenario, you probably should be checking your entire range. When you check, you pass the action to the original raise, who can also check and see the Turn card or bet, in which case the actions come back to you, and you can decide whether you want to fold, call, or raise that bet.