Data labels make a chart easier to understand because they show details about a data series or its individual data points. For example, in the pie chart below, without the data labels it would be difficult to tell that coffee was 38% of total sales. You can format the labels to show specific labels elements like, the percentages, series name, or category name.
To format data labels, select your chart, and then in the Chart Design tab, click Add Chart Element > Data Labels > More Data Label Options.
Click Label Options and under Label Contains, pick the options you want. To make data labels easier to read, you can move them inside the data points or even outside of the chart.