I downloaded the demo and it has no instructions. I have no idea how to attack enemies.

Good point, I'll make an instructions file and update it pretty soon. For now:

(Note: I just realized you said the Demo version, some of these commands didn't exist at that time. Mostly just the running and blocking based commands.)

WASD - Move
E - Interact (Open doors, read books, buy items, etc.)
F - Attack (in the direction you are facing)
Q - Use Item (read scrolls, if you have one)
Shift - Run, Charge Magic
Tap Shift quickly - Next spell (if you have one)
Release Shift (with magic charged) - Fire Magic
Right Click - Block
Right Click (while running) - "Dodge roll" (more like a quick dash atm)

I'll probably be remapping this a bit for the next update, since right now you can't charge magic without running, which feels a little strange.