"We" sort of understand, theoretically, what the electric and magnetic forces are, and have gotten somewhere with manipulating them.
Gravitation is a different matter. We can describe it (inverse square law, general relativity), but don't (that I'm aware of) have a theoretical description of what causes it. Manipulating gravity (the way we manipulate electricity and magnetism) depends on better theoretical understanding of what gravitation "is".
Understood. Electricity is bi-polar and everything has a specific gravity. Gravity itself is mono-polar and has no mass, nor specific gravity since it is not a particle but a phenomena. Much like centrifugal force does not exit, but centripetal does, gravity cannot be studied directly but only by inference.