It's YOUR story. You've already invented fictitious aliens. Now you can go ahead and make up all the fascinating details of why they're here, where they live, what they eat, what they like to do in their spare time, how they like it here, what they do when it's raining, what their plans are, what they think of us, and why nobody has ever seen or heard one.
Gravitational field strength is the force experienced by a unit mass. Gravitational force is the amount of force acting on a body. It is the product of field strength times the mass under consideration. Gravitational pull is just a more colloquial name for gravitational force.
