The rules in this game are very similar to Texas Holdem, or Texas Hold'em.
Omaha is usually played in Hi/Lo variation, meaning the pot is split between the highest hand and the lowest hand
If you do not have an 8 or lower among your four hole cards, you cannot qualify for low.
If three or more cards 8 or lower do not end up in the community cards, there is no possibility for low. In that case, the pot will not be split (unless two hands will tie for high).
Aces are either low or high. Straights and flushes do not count for low.
Also see: オマハ - 日本語 | オマハハイロー - 日本語