Players are dealt 4 cards. There are four betting round (preflop, flop, turn, river). All cards A,2,3,4,5,6,7,8,9,10,J,Q,K can make a high hand.
A,2,3,4,5,6,7,8 can make low hand. At the end of the hand 2 of your cards and 3 cards from the board make your best high hand possible. When a low hand is possible, 2 low cards of yours (can overlap with high-hand cards) and 3 low cards from the board make your best low hand possible.
A bit more detail:
-Every player is dealt 4 cards (instead of 2, which is in Holdem)
-There are four betting rounds, just like in Holdem (preflop, flop, turn, and river)
-The 2 cards that make the best high or low hand are used. So, a hand like A,A,A,A is a very bad hand, because only two cards can be used.
-The players with the best high hand, and the best low hand split the pot. Although, sometimes a player has both the best high/low hand, and takes the whole pot. Or a player has the best high hand and ties for best low hand, so they get three quarters of the pot (all of high, half of low).
-Cards that can be used to make high: ALL CARDS. By all cards, I mean any of the cards in a deck can be used (A,2,3,4,5,6,7,8,9,10,J,Q,K any suit).
-Cards that can be used to make low: A,2,3,4,5,6,7,8. A is the best low cards, while 8 is the worst.
-Best possible high: A,K,Q,J,10 suited, which is just like Holdem.
-Best possible low: A,2,3,4,5. This is also a pretty good high, as well. As, it is a straight: A-5.
-Hands that give you both a good high and low hand are best. They are even better when double suited (two pairs of suited cards)
Examples: A,A,2,3 double-suited. A,2,3,4 double-suited. Gives you several low chances (with 3 (1st one) or 4 (2nd one)very low cards, in case 1 of them appears on the board). Gives you several high chances (straight flush, 4 of a kind, flush, straight).
-Low hands are much better than high-only hands, as each hand there is about a 60% chance a low hand will be possible.
-There are not too many playable high hands, as in most cases you either gonna lose the hand, or only win half of the pot. Some high only hands that are playable include: A,A,K,K and K,Q,J,10. Hopefully these hands are double-suited, which gives you a better chance of winning high. With even some of the best high-only hands, watch out, because when there are large pots preflop, it might not be worth in to be in them, as there not too profitable, unless the board shows no chance of getting a low (2 or less low cards that are different).
Hope this helps, and if your still unsure about anything about omaha high/low, contact me by private message, or just ask it in this thread.