How do I link to a tab / page /subpage in my guide?
Just go to the page you want to link to and copy the URL from the address bar. Each page URL is unique and permanent, yet separate from the "friendly" URL. If you look at the URL for any page in any guide, it contains two pieces of information: pid refers to the overall guide, and sid refers to each individual page within the guide.
For example, this link is for the Customize Your Profile page in the Introduction to LibGuides guide in the Help system: http://help.libguides.com/content.php?pid=34814&sid=255988