Weight is a measure how heavy something is. How heavy something is depends on two things. One of them is gravity. Something that is heavy on earth might be lighter on the moon as moon has less gravity than earth.

The other one weight depends on is how much mass there is in the object. More mass then more weight.

Because weight is a measure of both mass and gravity one uses a "spring balance" to measure weight. A "spring balance" tells us how much force is applied on the string. This force is proportional to the mass and also the gravity and hence is a measure of its weight.