Let Excel be your calculator
With a simple formula, Excel can perform calculations on numbers using operators, such as the plus sign, and functions, such as SUM.
To add numbers, you use the plus sign (+). A formula always starts with an equals sign. Then type a number, a plus sign, another number, and then press Enter, and the cell displays the results.
Subtracting is similar to adding, except you use the minus sign (-). Click a cell, then a minus sign, then another cell, and press Enter.
Multiplying is similar to adding or subtracting, except you use an asterisk (*). Click a cell, then an asterisk, then another cell, and press Enter.
Dividing is similar to multiplying, except you use a forward slash (/). Click a cell, then a forward slash, then another cell, and press Enter.
Click the cell to the right of a row or below a column. Then, on the Home tab, click AutoSum, verify that the formula is what you want, and click AutoSum again.
AutoSum adds the row or column automatically.
Excel uses the standard math rules of operator order in formulas. Calculations in parentheses are evaluated first, inner to outer if they're nested. Exponents are evaluated next, then multiplication and division, working from left to right. Last in operator order are addition and subtraction, working from left to right.