Using the L Gear

If I move my shifter past D on my 2011 Enclave CXL it goes to L. Then I can use the button on the shifter to switch between 2nd and 3rd an so on.

How do you properly use that? I never learned to drive a shift clutch. Is there a chart or graph that will tell me when to shift at a certain mph? Like 2nd is 10 to 20 mph and so on?