A formula starts with =

=B2*C2
=SUM(B2:B20)
=AVERAGE(C2:C20)

Why your formula broke when you dragged it

References are RELATIVE by default. Drag =B2*C2 down and it becomes =B3*C3, which is usually what you want. But if part of the formula must always point at ONE cell (a VAT rate in E1) that reference has to be locked.

=B2*$E$1

$ before the letter locks the column; before the number locks the row. $E$1 locks both, so it stays put however far you drag.

Pressing F4 while editing a reference cycles through the four combinations, much faster than typing the symbols.

Ranges

• B2:B20, a block
• B:B, the entire column, which grows as you add rows

Do not hardcode numbers into formulas

=B2*0.16 means finding every formula when the rate changes. Put the rate in a labelled cell and reference it. The sheet becomes something another person can safely change.