When you Copy and Paste a cell that has a formula, the cell references change relative to the formulas new location. This enables us to replicate formulas across rows and columns which in most cases is exactly what we need.
Sometimes however, we simply want to copy and paste a formula and use it as a starting point for a similar formula in a new location and keep the cell references as they are. To do that:
Select the cell that has the formula you want to copy.
Press F2 or double-click to enter Edit Mode.
Press ctrl-A to select the whole formula.
Press escape (top left on your keyboard) to exit Edit mode.
Select the cell that you want to copy the formula to.
Press ctrl-V to paste the formula in its new location.