An absolute reference does not change when you move or copy a cell. We use the $ sign to make an absolute reference – to remember that, think of a dollar sign as an anchor.
For example, enter the formula =$A$1 in any cell. The $ in front of the column A means do not change the column, the $ in front of the row 1 means do not change the column when you copy or move the cell to any other cell.
As you can see in the example below, in cell B1 we have a relative reference =A1.When we copy B1 to the four cells below it, the relative reference =A1 changes to the cell to the left, so B2 become A2, B3 become A3, etc. Those cells obviously have no value inputted, so the output is zero.
However, if we use =$A1$1, such as in C1 and we copy it to the four cells below it, the reference is absolute, thus it never changes and the output is always equal to the value in cell A1.