When two or
more gravitational forces act on a body then the resulting effect on this body
is analysed by principle of superposition of forces which is stated as the
effect is considered by resultant force on the body calculated by vector sum of
all independent gravitational forces acting on the body. See the video below to
understand the principle of superposition of gravitational forces:

For
understanding the application of principle of superposition, see the example
videos below:

Introduction
to Gravitational Field: The region in surrounding of every mass is the
gravitational field, which is defined as a region in which any particle or
extended body having mass experiences a force on it. The magnitude of the force
per unit mass is defined as the gravitational field strength at a specific
point in space of gravitational field region. To understand the basics of
gravitational field, see the video below: