What are the general functions of a mitochondria

Produce the energy currency of a cell.

Other than being "the powerhouse of a cell", a mitochondria is responsible for ATP synthesis and cellular respiration, which occurs in the mitochondrial matrix. Various ATP molecules would be used in phosphoryllation which catalyzes enzyme and cell activities. In our cells, it has an even bigger effect, through chemiosmosis or also known as oxidative phophoryllation, where various ATPs are formed after glycolysis