In chess, each piece has a relative value, or point value, that helps players determine whether to capture a piece knowing that the piece that does the capturing will also be captured. So for example, if you capture a Knight with a Rook and know that the Rook will be captured you are losing 2 points since the Knight you captured was only worth 3 points and the Rook you will lose in the trade is worth 5 points.
The values are:
Pawn: 1 point
Knight: 3 points
Bishop: 3 points
Rook: 5 points
Queen: 9 points
King: Invaluable
Explanation
Pawns: Pawns are worth one point because they can only move in straight lines, either one or two squares on their first move.
Knights and bishops: Knights and bishops are worth three points each, so trading one for the other is considered an equal trade.
Rooks: Rooks are worth five points.
Queens: Queens are worth nine points because they can move in all directions.
Kings: Kings are considered invaluable because they can't be captured, and checkmating the king is the goal of the game.
Piece values are a rough guide and can vary depending on the position.
Knowing the value of each piece can help players decide whether to trade pieces.