To enter a basic formula in Excel, enter an equal sign into the cell where you want to place the formula. This signals to Excel that the following input is formula input. The formula itself varies depending on the type of function and whether it is a mathematical operator.
Mathematical operator formulas are simple and use the operation symbols after the equal sign. For instance, the plus sign signifies addition, while the hyphen, or minus sign, signals subtraction. A forward slash signifies division, and an asterisk signals multiplication.
Most formulas use a series of cell references containing values to automatically calculate answers. Other formulas require a built-in function, such as the word SUM or AVERAGE. All formulas automatically update the answer when the value of a cell reference changes.
As an example, to multiply the contents of cells A2 and B2, select cell C2 and type an equal sign to start the formula. Next, type the cell names separated by the operation symbol for multiplication with no spaces. The formula should look like "=A2*B2."
Alternately, select cells in the worksheet while you have the formula cell selected. The formula auto-populates the field with any selected cells. Instead of typing the entire formula, type an equal sign, and then click A2. Type an asterisk, and then click B2.