There are two ways of using cells in formulas: relative and absolute.
Relative references (to cells) change when a formula is moved to another cell. This is a powerful feature as it saves you having to work out a different formula for an identical calculation.
Absolute references to cells will always refer to exactly the same cell, even if the entire formula is moved or copied to another cell. This is powerful: change one cell's value and see its impact!
There are two main types of formula that you can use in a spreadsheet: logic and mathematical functions, although they are not the only types.
Logic functions help the spreadsheet decide how to act. For example, the IF function. Mathematical functions use data in the spreadsheet to calculate numerical answers. For example, the SUM function.