Answer:
Humans need food from the outside to obtain energy. Cells seek their energy in the form of nutirents that can come in many forms including sugar and fats. Due to some chemical processes the necessary energy is obtained to carry out all cellular functions.
The difference is that:
-Fats are used for long term energy storage because it is hard to break down them, they are complex molecules which requiere more amount of energy to break these bonds.
-ATP molecules can be broken down in a very short time, that´s why they are used for example while doing short bursts of exercises (inmediate energy is required). ATP readily dissociate into ADP and Pi and this process releases energy