The rules of Omaha

Omaha is a lot like Texas Holdem in using a three-card flop on the board, a fourth  and fifth board card. Each player is dealt 4 holecards (instead of 2) at the start. In order to make a hand a player must use exactly  two hole cards with three boardcards. The betting is the same as in Texas Hold'em. At the showdown, the entire four-card hand must be shown to receive the pot.

Omaha rules are exactly like Texas Holdem except the rule on playing the board, it is not permitted in Omaha (you must use two cards from your hand and three cards from the board).

Omaha High Low
Omaha is often played high-low split, 8-or-better. The player has to use a combination of two holecards and three boardcards for the high hand and another (or the same) combination of two holecards and three boardcards for the low hand.

In Omaha High Low,  a qualifier of 8-or-better for low applies to all high-low split games, unless a posting to the contrary is displayed. If there is no qualifying hand for low, the best high hand wins the whole pot.