What is gravitational field and gravitational potential ?

gravitational field at a point is the force experienced by a unit mass placed at that point. Its direction is  towards the center of the mass causing the gravitational field.  units are newtons per kilogram (N/kg) in the International System of Units (SI)

it is a vector quantity

Gravitational potential

It is defined as the amount of work done to move an object from a reference point (often infinity) to a specific point in the gravitational field

it is a scalar quantity 

Gravitational field      A gravitational field is the force field that exists in the space around every mass or group of masses. This field extends out in all directions, but the magnitude of the gravitational force decreases as the distance from the object increases.   Gravitational potential   Gravitational potential is a scalar field associating with each point in space the work (energy transferred) per unit mass that would be needed to move an object to that point from a fixed reference point. It is analogous to the electric potential with mass playing the role of charge. The reference point, where the potential is zero, is by convention infinitely far away from any mass, resulting in a negative potential at any finite distance.   In mathematics, the gravitational potential is also known as the Newtonian potential and is fundamental in the study of potential theory. It may also be used for solving the electrostatic and magnetostatic fields generated by uniformly charged or polarized ellipsoidal bodies.

Gravitational field : it's a force of an earth aroound

It increase with decrease of square distance. 

Gravitational potential: relating to gravitational field earth is like to be a source charge any object in the field is point charge it moved towards source with energy it is gravitational potential. How much energy is required to move is gravitational potential

It increase with decrease in only distance.