From the FAQ library
Chinese Mahjong
To win, you need 14 tiles that form four sets (chows, pungs, or kongs) plus one pair, and your hand must score the minimum required fans, typically 8 fans in standard MCR play. You can win either by drawing the winning tile yourself from the wall (self-draw) or by claiming another player's discard as your final tile. The hand is then declared, fans are counted, and payment is collected from the other players.