Hello! Can someone please explain to me the concept behind the adjoint representation of a Lie group? I have run through the theory but I ma not quite getting it.

In my book the author gives such definition

''Take any and define homomorphism by conjugation

This homomorphism is called the adjoint representation of G''

What does it do?

I have also noticed that there is also an adjoint representation of a Lie algebra? what is the difference?

Thank you