Morning Chris
The only silly question, is the one you dont ask!
As you say having a reg fitted gives you consistant power on a pcp.
Tuning a rifle basically means having it smoothed out.
Tuning can be anything from dampening the recoil of a springer to increasing the power, simply making the trigger mech more smooth and crisp is also classed as tuning.
Its something that you can do yourself, like polishing up the sears, changing the lube for a better one or if you prefer not to do it yourself, get a smith to do the work for you, A&M seem to be the best as well as Sandwell F