Mapping gives you the ability to send variables to the UI from actions taken on a controller and map a keyboard key for a controller button or axis.

The windows have to lists you can change between, one for variables and one for keys. 

Click add at the bottom of the window to add a new line, then enter the name of the variable you are creating and press ok.

After creating the variable double click on the line to activate input binding from a controller. If successful the input and controller column will show what controller you used and button.