Numbers in Excel can assume many different formats: Date, Time, Percentage or Decimals.
To Format the Appearance of Numbers in a Cell:
Select a cell or range of cells.
Choose Format Cells from the menu bar.
You could also right-click and choose Format Cells from the shortcut menu.)
The Format Cells dialog box opens.
Click the Number tab.
Click Number in the Category drop-down list.
Use the Decimal places scroll bar to select the number of decimal places (e.g., 2 would display 13.50, 3 would display 13.500).
Click the Use 1000 Separator box if you want commas (1,000) inserted in the number.
Use the Negative numbers drop-down list to indicate how numbers less than zero are to be displayed.
Click the OK button.
Use the Decimal places scroll bar to select the number of decimal places (e.g., 2 would display 13.50, 3 would display 13.500).
Click the Use 1000 Separator box if you want commas (1,000) inserted in the number.
Use the Negative numbers drop-down list to indicate how numbers less than zero are to be displayed.
Click the OK button. Cells from the menu bar.
The Format Cells dialog box opens.
Click the Number tab.
Click Date in the Category drop-down list.
Select the desired date format from the Type drop-down list.
Click the OK button.
Formatting Time in the Format Cells Dialog Box
The time can be formatted in many different ways in Excel 2003. Here are a few ways it can appear:
13:30
1:30 PM
To Format the Appearance of Time in a Cell:
Select the range of cells you want to format.
Choose FormatCells from the menu bar.
The Format Cells dialog box opens.
Click the Number tab.
Click Time in the Category drop-down list.
Select the desired time format from the Type drop-down list.
Click the OK button.
Formatting Percentage in the Format Cells Dialog Box
There may be times you want to display certain numbers as a percentage. For example, what percentage of credit cards bills account for your total monthly expenses?
To Express Numbers as a Percentage in a Spreadsheet:
Select a cell or range of cells.
Choose Format Cells from the menu bar.
The Format Cells dialog box opens.
Click the Number tab.
Click Percentage in the Category drop-down list.
Define the Decimal Places that will appear to the right of each number.
Click the OK button.
Look Up!
Open your Monthly Budget file.
Format the numbers in the spreadsheet as Currency without the $ symbol.
Fill the formula from B19 to C19 through N19. This text will appear in cell 19 of Columns D through N because expenses have not been entered for those columns yet.
Select Row 19 and format the numbers as a percent with no decimal places.
Cells from the menu bar.
will appear in cell 19 of Columns D through N because expenses have not been entered for those columns yet. 
Save and close the document.