How can I add subscribers to a specific group on newsletter signup?

I just installed the e-newlsetter plugin and I was hoping to be able to give users a choice of lists they want to be subscribe on at the very begining.

I can see that I can create groups, but I dont want to add people to groups AFTER they signed up, but let them check what group/list they would like to sign up to.

How do I do that?
Thank you,