How does fermentation differ from respiration?

Fermentation doesn't need oxygen in its process while respiration needs oxygen.
Fermentation is also known as anaerobic respiration and respiration is known as aerobic respiration.

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.