Relationship between pseudo random function (PRF) and pseudo random generator (PRG)?

I am currently learning for my crypto exam and I dont really get the relationship between pseudo random functions (PRF) and pseudo random generators (PRG).

For both it should apply that a distinguisher cant distinguish between an output generated by PRG/PRF and a truly random function. Is my thinking correct, to get a PRG I can use a PRF? I know that deterministic implementations of PRGs would be by using blockciphers for example...

Can someone explain me the relationship/difference pls?