How to Type a Formula Manually in Excel for Mac 2011
Cell formulas are equations that perform calculations or logical operations. In Excel in Office 2011 for Mac, you can enter a formula on your own, or you can use the Formula Builder. When learning to type your formulas in manually, you can start with a very easy example to show the structure of a formula and that Excel treats numbers as values within a formula:

Start with a blank worksheet.

Type =1+1 in cell A1 and then press Return, Enter, Tab, or an arrow key to exit the cell.
If you select the cell again, you see that Excel displays the value (2) of the formula in cell A1 and displays the formula (=1+1) in the Formula bar.
The cell’s appearance changes while you type. Observe and see how the cell appears while you type and after you exit the cell. You can use the value represented in a cell and refer to it in a formula in a different cell.
Here’s another example. This time, use values from cells in the worksheet instead of using numbers in the formula. This gives you experience figuring out various ways to refer to cells and cell ranges in formulas:

Start with a blank worksheet.

Type 1 into cells A1 and B1.
The value of 1 displays in cells A1 and B1.

In cell C1, type =A1+B1.
Excel colorcodes the cell references within your formula to match the referenced cells A1 and B1, which are now highlighted to match the color code in the formula. Your formula now displays in the Formula bar.

Click the green Enter button when done.
Excel displays the value of the formula in cell C1 and displays the formula in the Formula bar.
The moment you start typing in a cell or the Formula bar, the red Cancel and green Enter buttons become activated. You can click Cancel to erase your cell entry or click the green Enter button to accept your entry. These buttons are new for Excel 2011.