Two matching free tiles make a pair.
A free tile: has no tile on top, even partly. Its left or right side must also be open.
One open side is enough; the left and right sides do not both need to be open. Neighbours in the rows above or below do not block a tile. A tile on a higher layer does block it if it overlaps, even partly. Both matching tiles must be free before your move.
Suit and number must match: Bamboo 3 matches Bamboo 3, but not Circle 3. Winds and dragons must be of the same kind. In Tenpai, Orchid matches only Orchid, and Winter only Winter.
Two matching free tiles are outlined in gold. The panel closes when you choose a pair so you can see both tiles. Tap the tiles yourself to remove them. Use Next pair to cycle through the available moves.
A hint shows a legal move, not a guaranteed route to clearing the board. In Game settings, you can enable automatic highlighting when you open hints.
Undo takes back a previous move. Shuffle rearranges the remaining motifs; removed tiles stay removed. Shuffling clears your undo history.