There are many variations of poker with most of the online sites offering you the chance to play several of the most popular. A few of these variations are briefly described below.
This is the most popular variation today due to the fact it is very easy to learn and start playing. Although it is easy to learn it is not as easy to master and it could take years to reach the level of professional players.
Each player is dealt two cards which they and they alone see. There are three rounds of community cards dealt face up for every player to use, five community cards in total. There is a round of betting after each round. The best five card hand using any combination of the five community cards and the two hole cards wins.
This is a variation on Texas Hold'Em but is played with four hole cards instead of two. At showdown, the best five card hand using two of your hole cards and any three cards from the community cards wins. The difference between Omaha and Hole'Em is that you must use two of your hole cards and not more than three of the community cards. The betting and the blinds are the same as Hold'Em.
This is a variant of Omaha with the betting and blinds being exactly the same. At the showdown, the pot is split between the holder of the highest hand and the holder of the lowest hand, if the low hand qualifies.
As in Omaha, each player starts with four hole cards and five community cards are dealt face up in the middle of the table. The difference with Hi/Lo is that each player can potentially have two different hands, a high hand and a low hand.
Each player forms a five card high hand by using only two of his hole cards with only three of the community cards. Each player also forms a five card low hand (if possible) by using only two of his hole cards together with three of the five community cards. Both the high hand and the low hand can use the same combination of cards but are unlikely to do so.
To qualify for a low hand you must have five different cards (no pairs) with no card higher than an eight. Straights and flushes do not count. The best low hand is A-2-3-4-5 of any suit. The hand is ranked by starting with the highest low card so 7-4-3-2-A, seven low, would lose to 6-4-3-2-A, a 6 low. If there are no qualifying low hands the high hand wins the entire pot.
Each player starts with two hole cards and one upcard. Then here are three more rounds of upcards and a final downcard. There is a round of betting after each card.
At the end each player is left with seven cards, four face up and three face down. The player holding the best hand using any five of their cards wins the pot.
This is a variant of 7 Card Stud with the betting exactly the same.
Each player starts with two hole cards and one upcard, there are then three more rounds of upcards and a final downcard with a round of betting after each. Each player ends up with seven cards, four face up and three face down and forms and high hand and, if possible, a qualifying low hand using any five of his seven cards. Both the high and low hands can use the same cards but don't have to.
At the showdown, the pot is split between the holder of the highest hand and the holder of the lowest hand, if the low hand qualifies.
To qualify for a low hand, a player must have five distinct cards (no pairs) with no card higher than an eight. Straights and flushes do not count.
This is the most famous of all poker games but is only played at a few of the online sites.
Each player is dealt five cards face down and then there is a round of betting. Next, each player now has the option to change between none and all five of their cards. The cards are discarded face down and players receive all their replacement cards in one go, also face down.
There is a final round of betting and then all the remaining players move onto a showdown.
Note: A lot of the internet sites have poker schools which allow you to learn the rules and most also allow you the option to play for fun so you can practice in real games without committing any money.