These processes require the creation of chemical bonds and the movement of matter - both of which can only take place if energy is supplied.
Of course, if your question is *how* do cells use energy then you need to study cellular respiration (also called the Krebs Cycle) and the role of ATP in energy storage.
In a muscle cell. Mitochondria are the parts of plant and animal cells, that take in nutrient and convert it into a usable form of energy. The energy is used to create a charge that expands and contracts the cell which will allow something like an arm to move. Muscles them selves would be floppy and bendable, it's the bone that is load bearing. This is just muscle cells and tissue, but every type of cell uses it's energy for different purposes, and in different ways.
Friction. Movement causes friction, a force that helps cells use their energy.
Space heaters.
To reproduce.
