Helen and Joe don't get much to do in When Harry Met Sally except dump Harry and Sally. Helen is Harry's ex-wife, who ran off with another man, and Joe is Sally's ex-boyfriend, with whom she had a conscious uncoupling. They're there to remind our protagonists of what they've lost.
Oh, and they also give both Harry and Sally a chance to freak out and lose their marbles upon learning of their exes' happy lives with people who are decidedly not them.
We don't learn much about Harry's and Sally's adventures in the dating world of New York City, but we do get to meet two of their SOs during the famous Pictionary scene. Harry's dating Emily—a famous baker who is maybe a bit too young for him. And Sally's dating Julian, who is maybe a bit too stuffy for her.
Sally's college friend—we forget her name—makes a brief appearance at the beginning of the movie, exchanging I-love-yous with Harry…
… Amanda Rice. That was her name. No, Reese. Amanda Reese. Yep, that was definitely it.
Elsewhere, Sally's friend Alice, whose name we do remember, pops up here and there to exchange banter with Sally and Marie. She's also the friend Sally describes to Harry when they first get together as friends. You remember: she's the one who got married, had kids, and then never had sex again.