!Newbie Helper:
Go and get a blue gem! *Don't you remember? You've got to kill Gremlins!*
As I said, move your cursor over a Gremlin and click the left mouse button. This will transform the cursor into the shape of a knife. Click the left mouse button again to attack.
Use *Soul Cry* magic before attacking. This will improve your chances greatly. To activate Soul Cry magic, press F2 key, and again to de-activate it.