Mah Jongg is a Chinese "card" game which is actually played with tiles. In some ways it resembles American games like rummy or poker, in that people try to build strong hands and bet on them. But in a couple of respects, Mah Jongg is meaningfully different from American card games.
At the beginning of the game, the four players build walls of tiles. The wall is then broken at a place determined by the roll of dice. The four players then draw hands, each in turn, from the wall, of 13 tiles apiece. The first player then draws a 14th tile, checks to see if s/he has a complete hand, then discards the tile least relevant to his or her hand. The next person takes a tile, checks the hand, and discards. And so on, until someone lays down a complete hand. It's possible that there is no complete hand after all the tiles are drawn, in which case the game is a draw, but that's fairly rare.
The main object of the game is to create a "complete" 14 tile hand consisting of three triplets and one pair. The triplets can either be three of a kind (hard to get), or three in sequence. The secondary object of the game is to make a "related" hand, with all triplets three of a kind, or all of one suit. Higher quality hands multiply the basic bet. On the other hand, they are harder to make, so it's often a question of bird in hand versus two in the bush.
In respect to winning, mah jongg differs from say, poker. In poker, there is a pre-determined number of rounds, and "best hand wins" at the end of so many rounds. In mah jongg, the winner is determined by "first past the post." ANY hand that meets the minimum requirements can be laid down to claim victory. Therefore, most players will rush to make the quickest winning hand, rather than a slow, high quality hand that might not be made quickly enough to win.
In poker, it would be as if the first person to make two pair (first past that post) can lay down his hand and declare mah jongg, thereby heading off the straight and flush draws that require five cards instead of four, thereby ending the game.