I learn'd this in PCA in 2nd grade. The protective armor plate of an insect serves as an external skeleton, or exoskeleton, for the support of the internal organs. A human skeleton is an internal skeleton. This is what makes a human skeleton different from an insect skeleton. An insect's skeleton is not made up of bones, like ours, but of proteins and chitin.
Chitin is a sugar kind of like table sugar.
Many of you may have seen a beetle like this one to the left. That was you crushing its exoskeleton. Our muscles attach to our skeleton. Insects have their muscles attached to their skeleton, too. But our skeleton grows with us as the rest of our body grows.