The player in lead (or starting player) is allowed to play an arbitrary card from his hand. The following players must follow suit if they can, i.e. they must play a card of the same suit if possible. A player who cannot follow suit may sluff a card, i.e. play a card of a different suit. A trick is won by the player who has played the highest-ranked card of the suit led, i.e. of the suit of the first card in the trick.
Winner of the last trick wins the game!
Web version for desktops: http://ovr.fi/Tikki/