The app, step by step. The rules are on their own page; this is what you'll see and what to tap.
Someone deals a game and picks Dominoes on New game — Block, or Draw if you'd like a boneyard. Say Deal me in. The table deals itself when everyone has answered.
Your tiles stand along the bottom. The line of play is in the middle, the two open ends ringed in gold. Above your tiles: the scores, and what just happened.
The tiles that fit light up. Tap one to lay it. If it fits both ends, tap it, then tap the gold end you want it on. Nothing fits? A Pass (or Draw a tile) button shows instead.
When someone goes out, or nobody can go, the hand is counted and the next one is dealt by itself. First to 100 (61 with three) wins — the results card shows the scores. Rematch deals the same table again.