How do I following up with contacts from Alpha Kappa Alpha Sorority, Inc.?

I am interested in one graduate chapter of Alpha Kappa Alpha Sorority, Inc. I've been to many of this particular chapter's events and have met and collected a few numbers from some of the members. I was told by one person that I have to get their contact information to follow up. I am not a pushy person by nature, actually I can be pretty shy at first. Now I am stuck when it comes to what to do next. After I get their contact information to follow up, what do I say? I've called a few and got their voice mails and left a message. Do I call back? how does this work? Help...:(