Mass is the amount of matter in an object. This amount doesn't change no matter where the mass is located. It can be on Earth or on the moon, but whatever the object's mass is, that would remain the same. However, weight is due to the affect of the force of gravity on an object. Weight can change depending on where the object is. Kilograms are a metric measure of weight. Someone can have a weight of 123 pounds. That would be their weight on planet Earth. However, on a smaller celestial body, such as the Moon, where the pull of gravity is one sixth that of Earth, their weight would be one sixth their weight on Earth. On a larger planet, like Jupiter, there weight would be much greater. Actually, even on Earth, at the equator their weight would be slightly different than at the poles. The closer they are to the gravitational pull, the more their weight would be. And since the Earth is not a perfect round object, but an oblate spheroid, the weight varies slightly where you are located on Earth.