How to downshift?

I have an '81 Passport that I recently bought and got running. This is my first 2 wheel ride with a shifter. I know how to drive a standard car, but I don't think much of it will transfer because of the semi-auto clutch.

I try downshifting at the lowest speed possible, but sometimes I need to downshift when climbing a hill. How do I downshift without a manual clutch and rev matching?