1. On the Index Calculator sidebar, in section 2. Regions, click Regions. The Region List pop-up appears.  
2. Click Add.

3. (optional) Double click on unnamed to edit the name of the region. 

4. Click OK.
5. The Region List pop-up is closed.
6. Click on Draw to start drawing the polygon region in the Index View for the selected region name.

In the Index View, left-click to place polygon vertices, and right-click to create the last vertex and close the polygon. Ensure that after drawing a region, the check mark  appears beside the button Clear.

7. (optional) Click on Regions... to display the area of the regions and the percentage each region occupies among all the regions.