This is a secondary component added to characters that can be used to generate body physics colliders by analyzing the skinned mesh of your character model.
There are a number of override settings to control how colliders are generated and the generated colliders can be modified after the fact to fix overlapping and other issues found in testing.
To generate colliders for a character, click the Genrate Colliders button. This will open a dialog window where you can choose between minimal, medium, and full colliders, as well as which skinned mesh renderers should be evaluated.
Click Generate Colliders & Import when you're ready. Note that you can always remove the generated colliders by clicking Clear Generated Colliders, so you can easily recreate them and try out different collider levels to see what works best for your character.