Witch Ocultist - Cold Snap Vortex question

Hello.

I am a new Path of Exile player and I have a few questions about my character I created. The problem is that I can't use the Frostbite skill because I reserve too much mana. I have seen many players who have three Auras Discipline, Enfeeble and just Frostbite enabled. I would like to ask for a hint on how to achieve it unless I misunderstand it. I would also like to ask for a hint how I can improve my gear because I have the impression that I was in progress.

My items


Don`t know how to link skill tree.