Each round begins by randomly dealing a number of cards (the non-deterministic element of poker). In some variants these are community cards which are shared by all players. Each player receives the same number of cards - each of which is either face-down (known only to this player) or face-up (known to all players). There are other possible dealing steps such as drawing (discarding and replacing face-down cards) and rolling (revealing some face-down cards). The face-down cards are the imperfect information of poker. Each player knows their own cards but not those of their opponents.
A variant can be defined by a script which specifies the number of rounds and what dealing actions are to be taken at each round. This script has one entry for each round in the variant (recall there is also a series of betting that occurs at the end of each round). Here are the scripts for some well-known poker variants:
Five-Card Draw (2 betting rounds):
Seven-Card Stud (5 betting rounds):