Think of voltage as electrical pressure; amperage as the volume of electricity flowing; and resistance as electrical friction that resists current. Direct Current or DC is electricity flowing from a battery. Alternating Current is electricity flowing from an alternating power source such as a stator.
The purpose of an internal combustion engine is to transform chemical energy into mechanical energy. This is accomplished by igniting an air/fuel mixture that causes a shaft to rotate. We then use this rotating shaft to create useful work.