Mail Chimp Groups Integration?

Hello,
I am trying to get Gravity form to send what my subscribers are wanting to subscribe to in my form over to mail chimp. I cant seem to figure it out. I found this post http://www.gravityhelp.com/forums/topic/mailchimp-groups where Carl Hancock explains there is a way to do it but he does not give step by step instructions. Can anyone give me instructions on how to make this work? Both instructions on what to do in wordpress admin and in mailchimp so when a user subscribes to some of my categories this is sent over to mail chimp? When I created my form in mail chimp I used the check boxes selection as the way for people to check what they want to subscribe to. Also if you go to this page of my site you can see the mail chimp form up on my site http://atlantagoldandcoin.com/blog/ on the right hand side I do not have the gravity form up on my site cause I dont want to show or use that until this is sorted out any and all help is appreciated.
Thanks