The card
In American Mah Jongg you cannot win with just any arrangement. Your 14 tiles must match one of the hands printed on the card. The card is a sheet of patterns, and a new one comes out every year. A card hand is a pattern; your hand is the tiles you hold.
Each hand is a list of groups. A is two alike. A is three alike. A is four. A is five. Hands mix these in set ways: maybe a pair of , a kong of 3 Bams, a kong of 3 Craks and a kong of 3 Dots, fourteen tiles in all.
Early in a game you look at your tiles, look at the card, and pick a hand to aim for. You will change your mind as tiles come and go. That is normal.
This site uses its own small practice card, so the skills carry to whatever card you own at the table.
A kong is how many tiles alike?