In PowerPoint, you can use category names, series names, or values as Data Labels within charts — more often than not, most charts show values as Data Labels — and values denote numbers! When you use numbers as Data Labels, you may want to format them for several reasons such as limiting or expanding the number of decimal digits shown, or including the currency symbol along with the values, or show the value in percentage etc.
Learn how to format Chart Data Labels (numbers) in PowerPoint 2011 for Mac.