The game of bridge is all about taking tricks. I assume that you are reading this page of the website because you don't know what a trick is. All of the whist based games use tricks and this is how they work.
With aces always counting high, a trick is won normally by the highest card as in the example here. North leads the Queen of Spades, East plays the King, South plays the Ace and West plays the four. South wins the trick as they have played the highest card.
The rules say that you MUST follow suit if you hold a card in that suit. If you don't you are said to have revoked and penalties apply. If you don't hold any cards in the suit being led you can throw any old card on it without penalty.
You can also play a trump card which is all powerful. Imagine you are sitting in the West seat and don't have any spades but diamonds are the trump suit. The play would proceed as above but when it was your turn you could play a very low trump, (say the two of diamonds), and that would beat all the other big spade cards on the table.
Tricks always go in a clockwise direction and everyone must play a card. For convenience players are known as north, east, south and west.
Whichever hand wins the trick also makes the next lead. This is critically important in the game of bridge but applies in all trick based games.