What is $ sign in excel formulas?
For example, if you have formula "=A1+B1" in cell C1, and drag it downward. (or copy the formula to other cells).
The values in column C will automatically equal those in column A + Column B.
please see the screen shot below,
If you add the dollar sign inside the cell A1 like A$1, and drag it downward, you will have the column C equal the value which is equal to A1+B1, A1+B2, A1+B3,... Etc
see that A1 is constant for all calculations.