classes v. functions

This may show my ignorance or my refusal to take for granted something I don't fully understand but I have a hard time figuring out the advantage of using classes as opposed to just functions. I am certainly new to php and at first sight classes seemed to cut a lot of corners but so do functions (with which I have more experience). The more I read about classes the deeper the confusion. Anyone can enlighten me? Regards, Andu Novac