Class VS Functions

Hi. I'm newbie in php (i'm in php about 1 year +/-), and after i read a lots of docs showing the possibilities in php coding with Class's but the true is that the "reability" of the code with Class's i steal can make the same with normal functions. I ask for the ppl, to give me examples (theorics preferencly) about situations that Functions cant handle with the job :\ Sorry my terrible bad english... Cláudio Franco