Instead of doing a tutorial as a separate section, have it part of the gameplay. You could put signs on the wall at the bottom to show what to do initially (movement, jump, and then grapple). 

I probably did what many people do and just clicked play, and couldn't get up to the first platform and didn't know about the grapple hook.

You could also make the grapple hook fire by default at 45 degree angles when you press the E or Q keys so that the game doesn't have to incorporate the mouse at all