How to use Absolute, Mixed and Relative cell references in Excel 365

Using $ sing - absolute cell reference in Excel

The dollar sign fixes the reference to a given cell no so that it remains unchanged no matter where the formula moves. In other words, using $ in cell references permission you to copy the formula in Excel without changing cell references.

 

Mixed Cell Reference in Excel
Absolute column and relative row, like $B2. When a formula with this reference type is copied to other cells, the $ sign in front of the column letter locks the reference to the specific column so that it never modified. The relative row reference, without the dollar sign, varies depending on the row to which the formula is copied.

Relative column and absolute row, like B$2. In this reference type, it's the row's reference that won't change, and the column's reference will.

Using F4 key to switch between the absolute, relative, and mixed references 

Through the F4 key to you must be able to modify  your formula like press F4 to toggle between four-cell reference types.