'You can add objects by opening them': UI unclarity / discoverability problem

[LinuxOnTheDesktop]

'You can add objects by opening them' - what, from within Library a.k.a. Thingy? There is no 'open' button. By opening them in another fashion while Thingy is open? Well, I opened something In Sublime, and no dice. Or, hold on, does what shows in Thingy depend upon which document type one has selected? Ah, it does. Discovering that last fact is not at all clear from the UI, especially because, e.g. 'Libre Office Calc' and (especially) 'Document viewer' are applications, not types of document.

In sum: it is hard for the user to discover how the Thingy program works.

In the same vein: a Thingy context menu has a 'move to trash' entry. Does that trash the actual file? Or does it merely remove it from the list of recent documents?