Honestly, read whatever guides, and talk to whoever, to get the basic idea of what's possible. You should understand the core concept of:
- pet fighting (charm mob A, make it fight mob B, break charm when they're both low and kill them ... ideally break charm using a Goblin Ghazughi Ring)
- quadding (snare four mobs, run in circles until they wind up on top of each other, use AoE spells and your Luminescent Staff to kill them all at once)
- root/rotting (this one you should use rarely, and doesn't require any special knowledge at all)
All that's worth learning from others, because not everyone thinks to do charm fighting or quadding on their own, and even if they do some details (eg. snare is essential for quadding, knowing about those two key items I mentioned) aren't immediately obvious.
But really everything else you can/should learn by
doing. Druids are not hard: go to the Per-Level Guide and filter for Druids, or use any of the lists in the Druid guides, and just get out there and start leveling!