If you don't want a number to be treated as a value that can be calculated (for example, an item number), you can format the number as text. It’s easy to tell at a glance if a number is formatted as text, because it will be left-aligned instead of right-aligned in the cell.
Select the cell or range of cells that contains the numbers that you want to format as text.
Tip: Although not always practical, it generally works best to format empty cells as text before you enter numbers in them.
On the Format menu, click Cells, and then in the left navigation pane, click Text.
Note: When you enter a number that begins with a zero, Excel deletes the zero by default. If this is not what you want, you can create a custom number format that forces Excel to retain the leading zero. For more information, see Use leading zeros in postal codes and other numbers.