We call it the Home Person. But you have to set a Home Person. And it can be changed easily.
While you’re becoming oriented, it may help to have browser bookmarks to the Visual Guide to the Gramps Interface and the Gramps Glossary. (The visual guide tells you our Terminology so you can look it up.)
But watching some of the tutorial videos is the quickest way to become productive. There are multiple ways of doing most things. So the tutorials may not show the method that is fastest, easiest, or best suited to your personal working style. It is just the method that video contributer likes.