If the first card played is trump, subsequent players must follow suit and also play a trump card that beats all previous cards if they can. It is called raising and applies only for trump suits. If non-trump was played first, and then trump, the player on turn needs to follow the suit of the first card played and doesn't have to trump the card that beats the first one. The player who won the hand or collects the cards played in this trick and plays first in next hand/trick.