Ugh, okay, so that's a super broad question because 'enchanted forest story' could be a million things. But if we're talking about THE enchanted forest story that immediately jumps to my mind, it's gotta be 'The Dark Is Rising' sequence by Susan Cooper, specifically 'The Dark is Rising' and 'The Grey King'. The key figures are Will Stanton, the last of the Old Ones, and Bran Davies, the boy with the silver eyes who's kind of a living part of the forest mythos. The forest itself, the Welsh hills, is practically a character.
Merriman Lyon is the mentor figure, but he's more tied to the overarching Light vs. Dark battle than just the forest. Honestly, the magic in those books feels so rooted in the land and ancient woods that the characters almost emerge from the trees and stones themselves. It's less about a roster of fantasy creatures and more about these human (and not-quite-human) vessels for the old magic.
If you mean something more traditional with fairies and sprites, maybe you're thinking of something like 'The Folk of the Air'? But for a truly enchanted forest, Cooper's work is where my brain goes first.