Work is movement against an opposing force. Mathematically work is equal to the magnitude of the force times the distance travelled. Heat is a form of energy. Heat is capable of doing work.
Heat flows from hotter body to a colder body.
Temperature is a measure of the direction of heat flow. Energy is measured in calories, or joules. The energy of the universe is constant. A substance is considered to be a fuel, if it produces energy. The most common energy producing reaction is the combustion reaction.