What is the diffrent between center of mass and center of gravity?

The terms "center of mass" and "center of gravity" are used synonymously in a uniform gravity field to represent the unique point in an object or system which can be used to describe the system's response to external forces and torques.

Center of mass is the physical center of an object. Center of gravity is where there is an equal weight on all sides. So if you had a piece of lumber that was 4 feet long and had a piece of steel attached to one end then the center of mass would be the 2 foot mark on the lumber but the center of gravity would be the point where the lumber could balance.

Mass is the amount of matter that a body contains, and a measure of the body's inertia, that is, of its resistance to change of motion.

Mass is different from weight, which is a measure of the attraction of the Earth for a given mass.

In short, mass is just the matter that a body has.

Center of gravity is totally different. It is a point at which the whole weight of the body seems to be acting. If you hold the object such that the imaginary perpendicular from the C of Gravity falls on your hand, then you will be able to balance it.

The centre of mass of a system of particles (or a continuous body) is the unique point at which the entire mass of the system (or body) may be considered to be concentrated.  For many purposes the system behaves as though the mass were concentrated at the centre of mass.

In a uniform gravitational field, the centre of gravity is located at precisely the same point as the centre of mass.  So, in most everyday scenarios, the centre of gravity is the same as the centre of mass.  If, however, a system is sufficiently large that the non-uniformity of the gravitational field experienced by the system becomes significant, then the centre of gravity will be slightly displaced from the centre of mass.