Dischage skill not working- Witch

Hi, I just received a new Discharge skill gem from a quest and I cannot get it to work. First time I haven't had a skill work. It is assigned to a key but when I press it nothing happens...

I am a level 31 Witch, I'm really stumped.

Please help if you can

Thanks!

You need either Power charges, Frenzy charges or Endurance charges for it to do anything. These can be achieved through various skills (Power siphon, frenzy, blood rage, enduring cry, warlords mark) and some items as well.

I had no idea. Thank you!!