To "compensate" means to add something in order to reach a balance. For example, if you injure one of your legs, you can use the other leg more in order to "compensate for" your injured leg.

People do a lot of things to "compensate" for their weaknesses. For example, a man who is short might "compensate" by lifting weights a lot and getting big muscles. Someone who doesn't feel confident might "compensate" by spending a lot of money on expensive clothes.