Use COUNTIF if you need to sum values for a particular person or other criterion.

Use SUMIF if you need to sum values for a particular person or other criterion.

There are several operators that could be used in formulas.

Applying a number format to a cell doesn't change the value, but only how the value appears in the worksheet. Formatting can play a joke with you, e.g., sum of values seems incorrect because Excel displays a limited number of decimal places and their sum is not equal to the real sum.

If you simply need to perform a calculation, you can use the Formula bar as a calculator.

Formulas can refer to cells in other worksheets-and the worksheets don't even have to be in the same workbook. Excel uses a special type of notation to handle these types of references.

You can enter nonrelative references (absolute or mixed) manually by inserting dollar signs in the appropriate positions, or you can use a handy shortcut - F4 key.

Range names is a powerful Excel feature which allows you to give a symbolic name for the cell or range of cells to be later used as convenient replacement for cell/range address in formulas.

If you would like to better understand how some of these complex array formulas work, consider using a handy tool - Formula Evaluator:

You can easily count the number of unique values of the range using a simple formula.