Reddit reviews The Field Description of Metamorphic Rocks

Whilst I don't know where you could learn online, I highly recommend looking up publicly available field courses in basic geology. You would learn alot and be able to go out hiking!

If you're interested in sedimentary geology, Gary Nichol's book is excellently written, organised, and I would say is very accessible by the layman.

I'd also recommend the different Geology Field Guide Books as they are small, easily looked through and designed to be taken into the field. They have one for sedimentary, igneous, metamorphic and structural I think, very good books that would definitely get you through at least the first 2 years of an undergrad bachelors in Geology.

EDIT: on further investigation I think I meant the Field Description book series. Either look pretty good for a basic grounding.

EDIT 2: I also forgot to mention they're relatively cheap compared to most academic texts!