Absolute Vs. Realtive
A absolute value is a value that is set and unchanging. Usually when a formula is auto filled into other cells during excel the values will change based on the locations of a cell. A absolute value will not. You can mark a value as absolute by adding $ signs in front of each value. For example: if my equation is =B1+E1 you can make B1 a absolute value by adding $ signs. Your new equation will =$B$1*E1. Now when auto filling the equations B1 will always be in the equation.
A relative value is a value that will change based on the cells location. Unlike a absolute value, a relative value will change when auto filled to other cells. Nothing has to be added to a value to make it relative. For example: Your equations is =B1+D1. When auto Filled to other cell the values will change because they are relative. If it was auto filled left 1 the next equation would be C1+D1.