When you type numbers in your worksheet, Excel Online automatically applies the General number format but you can change this to show specific number formats like dates, currency, or even fractions.
For example, if you’re working on your quarterly budget, you can use the Currency number format to show your numbers as monetary values. You can set dates to display either as a long date like Saturday, December 14, 2013 or a short date 12/14/13. Here’s how:
Select the column, or cells you want to format.
Click Number Format and pick the format you want.