Athlete's foot is caused by a microscopic fungus that lives on dead tissue of the hair, toenails, and outer skin layers. There are at least four kinds of fungus that can cause athlete's foot.
Work. In order to accomplish work on an object there must be a force exerted on the object and it must move in the direction of the force. Energy is required to do work and the basic SI unit of energy is the joule, the amount of energy required to exert a force of 1 Newton through a distance of 1 meter (1 joule = 1 newton meter).
To truly build then entire thing you need skills in both mechanical and electrical. Engineering is done in a team though. So you'll pick one area to be very skilled at, then the rest you'll need a basic understanding of. You're colleagues will fill in the other expertise.