The basic distinction
Standard four-card Omaha gives each player four private cards. A final hand must use exactly two private cards and exactly three community cards. Do not import Hold’em’s flexible selection rule into Omaha.
Check the variant
Omaha high, high-low and formats with different private-card counts require their own instructions. Confirm the version, hand-ranking system and limits before your first session.
Make the selection visible
In a practice exercise, place the two selected private cards apart from the three selected board cards. Say where each card came from before evaluating the hand.
Use the example carefully
The example below identifies a possible selection; the other cards from a full deal are omitted. It teaches selection, not a complete round or a result prediction.
Reference
https://www.pagat.com/poker/variants/omaha.html
Study the five cards.
Example selection: hole cards 3D and 4D; board cards 5D, 6D and 7D. Other dealt cards are omitted here.
These are five-card studies, not complete deals.