Tap three tiles, then pass them.
Before a single tile is drawn, an American mahjong hand is shaped by the Charleston: three tiles to the right, three across, three to the left — and in many games a second time round. This trainer drills the only decision that matters in it: what to give away.
You are dealt thirteen tiles and shown a line — five groups, the shape of a finished American hand. Choose three tiles and pass them right; the table passes three back. Then three across, then three to the left. Some levels run a second Charleston, so the same three directions come round again.
The tiles that come back are not random noise. Most of the time the table sends you something your line still needs, and sometimes it sends junk — the same mix you get at a real table, where you cannot control what arrives and can only control what you keep. Every time you pass, the trainer tells you how many of the three tiles your line actually needed. That number is the whole lesson.
When the passing ends you are scored on how many of your thirteen tiles belong to your line: twelve or more earns three stars, ten or more earns two. The lines used here are generic hand shapes — consecutive pungs, runs through the suits, winds and dragons, even and odd numbers — not the National Mah Jongg League card itself, which is published each year and governs real play. Your stars and unlocked levels are remembered on this device.