What lens would be good for the Olympus E300 DSLR? For portraits.?

I am confused on what lens to buy. I only have minimal expierence with SLRs in the first place.

I have a Olympus E-300 Digital SLR and I was wondering what lens I should I buy? I am going to be taking potraits, so what lens what be more benefical for what I'm going to be using the camera for

Thanks

I wish I could be more specific but I have always heard that a telephoto lens is good for portraits. It has something to do with the focal range.