The major differences between PL Omaha and NL Hold'em are three-fold. Firstly, you get four hole cards rather than just two. Second, you cannot go all-in at any time because the size of your bets and raises is capped at the size of the pot. Third, you must use exactly two of your down cards along with three community cards to make your final five-card poker hand. If you have the lone Ace of suit matching the suit of four board cards, you DO NOT have a flush.