How to organize my materials

Excuse me for posting a bunch of questions, I seem to be unable to find answers elsewhere. Coming from keyshot I'm used to build a library of materials inside the application. In Stager it seems I can only have the starter assets and create my own library that lives in the cloud.

I can't drag materials from the Project Materials to my library and the "+" at the bottom of the library list is inactive so can't add anything that way. The only thing that works is downloading materials to my computer and dragging them to my library. However, as I have written in another post, they show up with generic icons and no preview.

Maybe I don't get the concept?