Hey bootzin !  I wrote the "GAME CONTROLS" section at the game page description, sorry if this isn't immediately visible from the "game jam submission" page ! I'll paste it down below for the convenience, hope this helps :) 

GAME CONTROLS: 

- WASD & Spacebar: movement & jumping.

- Left Mouse Button (click&hold/release): choose your left hand spell.

- Right Mouse Button (click&hold/release): choose your right hand spell. 

- Middle Mouse Button (or Shift+Spacebar!):  CAST THE JOINED SPELL.

NOTE: Your spell casting will fail if you don't have both left and right spells chosen, which will be indicated by a visual cue and a (broken xD) sound.