Mass (measured in Kilograms) is the amount of matter there is, which generally corresponds to its physical size. An elephant is made of more matter than I am, so has a bigger mass.
Weight is a force (measured in Newtons) due to a mass being “pulled” by gravity.
So what’s gravity? It’s an attraction between ANY two masses. The bigger the mass, the bigger the force. The closer the two objects, the bigger the force. But the attraction between most objects is actually TINY! The only reason you notice the gravity of Earth is because the Earth is HUGE, and therefore has a really big MASS!
I weigh less on the moon than I do on Earth because the moon is smaller, therefore has less mass, therefore has a lower gravitational attraction.
Although weight is proportional to mass, they are NOT the same thing!
Saying that, you DO weigh yourself on scales, which tends to give you a measurement in Kg! Confusing huh?! By standing on the scale, you are compressing springs, and it is actually measuring the gravitational attraction of your mass to the earth!! The earth is pulling you towards its centre, and by doing so, it’s compressing the springs! The scales then just convert this into a mass, as obviously gravity is the same where ever you are on the Earth’s surface…
To prove this, take your scales to the moon! They would then tell me I’m 9kg!!!