Weight
You've gone to the doctors office and heard your doctor say "Okay I have to take your weight now" but what is weight? Weight is caused by gravity. Why do you think when astronaut go into space they become "weightless" thats because in space there is no gravity so there can't be any weight. Also if you were an atronut, and landed on the Moon, you would way then on Earth. That seems silly, Why would that happen. Well, because the moon has less gravity then the Earth, so there is less of the magical force that keeps us on the ground. You measure weight with a scale.
Mass
Mass and weight are similar but they are NOT the same. First, what is mass? Mass is here to measure how much stuff something has and can put into its self. You can measure mass with a fancy thing called a balance. Balances measure in grams and in kilograms.
This is what a balance looks like.