Ah, I see. Of course that makes sense - forgive me if I sounded dismissive, I didn't intend to. I was assuming you're studying with an order; in my case, the study materials for each grade themselves outline the basics and provide at least one or two methods as examples to follow in crafting our own versions of working. If I didn't have that as a source, I'd be quite lost.
If you're with an order that doesn't take the same methodology in their lessons, it might be they either provide a lot of reference points in their supplementary materials, or they may provide recommendations for further reading? Or, of course, you may not have chosen to join an order, and if you're solitary by choice you'd naturally need references from other sources.
Also I must sheepishly admit I do have Celtic Tree Magic; my mom got it for me awhile back, but it's been so long I don't recall its substance.
Idiotically, I didn't even remember Danu Forest until you mentioned her shamanistic aspect.
Anyway, best of luck to you!