An absolute reference in a formula does not change when the formula is copied or filled.
An absolute reference uses $ signs,
=$B$1 the column and row do not change.
=$B1 the column does not change
=B$1 the row does not change

Addition, subtraction, multiplication and division.
Addition: =B1+B2
Subtraction: =B1-B2
Multiplication: =B1*B2
Division: =B1/B2

Calculate the commission on sales.
=A2*B2
where A2 is the rate of commission (entered as a percentage)
B2 is the amount of sales
