Mana in my eyes is the energy required to use magical spells, It can be required by learning how to generate mana or just use mana-crystals, This mana has use for spells of a large magnitude.
You'll either need a large mana pool and be able to regenerate mana, For if so, You can use spells a lot faster, Or you can just use mana-crystals to make the pool deeper and more filled.
Use of Magic
The type of magic that you'll need mana for is combat magic, Like arcane, shadow, fire, frost, light, elemental, demonic.
Idea of my type of mana
My type of mana was inspired by World of Warcraft's mana, In which is used for any spell.