### Understanding the Difference Between Formulas and Functions

In Excel, you can perform calculations in two main ways, each of which starts with an equal sign:

*By using a function.* A *function* is a preset calculation that performs a standard calculation. For example, when you need to add several values together, you use the SUM() function—for instance, **=SUM(1,2,3,4,5,6)**, which is simpler than **=1+2+3+4+5+6** but has the same effect.
*By using a formula.* A *formula* is a custom calculation that you create when none of Excel's functions does what you need. The word *formula* tends to sound imposing, but a formula can be a simple calculation; for example, to subtract 50 from 100, you can type **=100-50** in a cell (the equal sign tells Excel you're starting a ...