The use of four identical tiles as a single Meld is called a Kan.
1. Closed Kan (when you have all 4 tiles)
2. Open Kan (when you steal the 4th tile)
3. Late Kan (when you draw the 4th tile and add to a Pon )
1. Declare Kans by stating "Kan" and revealing all four tiles.
2. Draw an extra tile from the Stock tiles.
3. Turn over an extra Dora (the Kan Dora).
Note: You may not Kan on the last tile (whether drawn by yourself or discarded by another player).