Hi and welcome to the InfoPath Dev forums,
What you want to do is actually pretty easy - you should be able to do this yourself.
We actually have a free template part that you can use, here is a blog about it and a link to download the XTP:
http://www.infopathdev.com/blogs/mel_balsamo/archive/2009/01/14/hide-show-section-template-part.aspx
I have also attached a very simple sample form so you can see how you can do this on your own - pay attention to the rules being used to set the "ShowHide" field value (that keeps track if a seciton should be shown or hidden and if the + or - button need to be hidden as well). Using conditional formatting you can easily show or hide a section based upon what value the users selects by pressing + or -
Hope this helps
Ted