The Gravitational Force is the tendency of masses to move toward each other. Weight results from the product of the force of gravity and the mass of an object. Exactly why two masses separated in space have a gravitational attraction to one another remains largely unknown, despite much research and various theories.
The Electromagnetic Force is a force that attracts two objects of opposite charge (or opposite magnetic poles) and repels two objects of like charge (or like magnetic poles).
The Weak Nuclear Force or weak interaction is one of the four fundamental forces of nature. It is most commonly seen in beta decay and the associated radioactivity. The predicate weak derives from the fact that the field strength is some 109 times less than that of the strong nuclear force. The term nuclear indicates that it is a short-range force, limited to distances smaller than an atomic nucleus.
The Strong Nuclear Force is the strongest of the four fundamental forces, with the shortest range of all. It holds the quarks together within protons and neutrons, and holds the protons and neutrons together to form atoms.