Tableau's default labeling of Pie chart is outside of the pie. But some may prefer to put the labels inside, which is not obvious.

There are 3 ways to do it, depends on what you need.

1.Static labeling

If you only want a screenshot or for presentation only, just drag the labels to where ever inside the pie chart. You can use this technique. Once the data change, the positions of the labels will change. So this won't work for dynamic data.

2.Labeling in the center

The method is to create two pie charts: one big and one small. Put the label in the center of the small one. Then lay the small it on top of the big one through dual axis. This kind of chart is called donut chart, such as this and this and this.
3.Labeling on the pie slices

Similar to the previous one, here are the major steps:
- Create a calculated field Zero which has value 0. Use it in Columns as discrete blue pill and twice in Rows as continuous green pill.
- Create one big and one small pie charts with the same dimensions and colors.
- Label the small one.
- Then lay the small one on top of the big one vis Dual Axis.
- Adjust the sizes of  pies so that labels are inside the big pie.
- Format the chart to remove the zero line.
Here are the views before and after dual axis.
4.Label inside donut chart
This is a variation of the 3rd. Just assign the same color to all slices, by using a duplicate dimension for coloring. We got this chart.
Voila! Click the above images to view the interactive version.