During a game of chess it is necessary and practical to exchange pieces with your opponent over the course of the game. The key to winning is to know which pieces to exchange with your opponent and when to do so. Every chess piece is given a relative point value, except for the king. In this value system pawns are worth one point, knights and bishops are worth three points each, a rook is worth five points, and finally a queen is worth nine points. Understanding the relative point values of these pieces will help you to determine if an exchange is worthwhile to you or not.
The main idea when exchanging pieces is to, at the very least, trade evenly valued point pieces. The best scenario though is to trade lower point valued pieces for higher point valued pieces. If you were able to sacrifice a bishop for a rook this would result in a point advantage to you of two points since the bishop is worth three and the rook is worth five points.
There are many schools of thought on when to trade a higher point valued piece for a lower one. One of these thoughts is that if you are trapped by your own pieces being in your way it is good to exchange pieces so that you have space to move your primary pieces. It is also commonly agreed on that if you are able to weaken your opponents pawn structure by exchanging pieces then you should do so. Always try to have the advantage, or more pieces than your opponent, after the exchanges take place. If you are able to sacrifice one piece, but win two pieces, then it is a good exchange. Use your skills to determine when you feel an exchange is warranted.