Questions: WordPress and MailChimp

Hi. I work for a small member-based non-profit arts organization. We have a WordPress website, where all our members are registered with the date they joined, their membership expiration date, and their contact info. The webmaster set it up so the members would automatically get an email a month before their memberships expired, with links for renewing on line. This system started malfunctioning, so our admin was supposed to integrate MailChimp with the website, so the renewal notices would go out via Mailchimp. Well, all she did was add the MailChimp plug-in and then she quit. So now I’ve been asked to figure out the integration, and due to a lack of sufficient experience I’m having a lot of trouble with this. The webmaster only helps us on a freelance basis and he’s too busy to help me with this. Can someone give me some “For Dummies” advice? Thanks. — Clare