I discussed compression a bit here:
I don’t know if that helps.
When to use things is tricky. Unless you are trying to replicate a particular tone/effect on a record, most of the use of effects is entirely artistic and down to artistic choices.
Describing and demonstrating the effects and giving examples of where they are used is, I suspect, all that could be done.
Justin did start a series a while back, and has covered delay quite well. It might be good if that series was expanded with other effects.
https://www.justinguitar.com/modules/all-about-guitar-effects
But it’s also worth exploring on your own, especially if you have a multifx unit, which are great for exploring different types and models of pedals without spending a fortune on individual pedals, struggling with cabling and power supplies, noise issues, etc.
The approach I suggest is to pick an individual effect type, turn it on and everything else off, and experiment with the controls and how it sounds. If there are multiple versions of that effect, try them out to see if you can distinguish between them. Often the differences are subtle, or some versions may give you more, or different, controls.
Spend about half an hour or so playing so you can understand what it sounds like and then go and do something else. Do this occasionally, visiting all of the main effect types, and you’ll get a good idea what most of them do.
Also, there’s a lot of info available on the Internet giving an overview, and there may also be some useful pointers in the GP5 manual:
Cheers,
Keith