Menus (from the menubar & right-mouseclick pop-up menus) & toolbars in Gramps are contextual. Until there is a tree & data in the tree, much of the interface is not enabled.
To try any of the examples in the online manual, you might want to import the example.gramps data into a newly created blank Tree database.
To save yourself a lot of confusion, maybe you’d find watching one of the tutorial videos on YouTube to be helpful.
The important thing to know about Gramps is that there is not just 1 way to do most things. You can build a tree from any number of starting points: a new person, a new family grouping, a source, an event, an import (even just from your phone’s contact list). And different way to start entering data for any of those starting points.
You use Gramps in the way that fits your workflow.
Add those add-ons you mentioned? They offer even more ways of simplifying tasks or adding more power.
For instance, the Data Entry Gramplet allows adding a person, establishing their relationship to the selected (Active) person, birth, death & associate a source for each in a single step. By default, you’d open an editor dialog for each of those elements.