OK... another newby here. How do you "experiment with climbing and
decending by using only the rudder pedals" when rudder controls yaw...
not
attitude?

Well, if you use the rudder you add a bit more drag.
Make some S's with rudder only and you will probably descent.
Another trick to make a light plane climb or descent is shifting your
weight by bending forward or backward. Works only if the plane is
trimmed properly and in calm air.

Try it,
Kees.