If a player discards a tile that you have a pair of, you may call Pong! and create an open Pong.
This open pong remains face-up in front of you, counts toward your winning hand, and cannot be changed.
If the player to your left discards a tile you need to complete a sequence, you may call Chow! to create an open Chow.
This open chow remains face-up in front of you, counts toward your winning hand, and cannot be changed.
If a player discards a tile that you have a triplet of, you may call Kong! and create an open Kong. Draw a replacement tile.
This open kong remains face-up in front of you, counts toward your winning hand, and can only be melded.
If you draw a tile that's part of your open Pong, you may call Kong! and add the draw to your existing Pong. Draw a replacement tile.
This melded kong remains face-up in front of you, counts toward your winning hand, and cannot be changed.
If you draw a 4 of a kind, you may call Kong! and create a concealed Kong. Draw a replacement tile.
This concealed kong remains face-down in front of you, counts toward your winning hand, and cannot be changed.
If you're 1 tile away from winning and someone discards the tile you need, you can call Mahjong! to win.