The IF function in Excel
The IF function checks whether a condition (or a set of conditions, when nested) is met, and returns one value if the condition is TRUE and another value if the condition is FALSE.
It allows you to create very complex formulas that can make your sheet do some extremely complex calculation.
Some easy examples, like checking who in a list of people is older than 18, or if a number is bigger or smaller than another.
=IF(test , value_if_TRUE , value_if_FALSE)