Welcome to the forum, nolalaura.
From your screenshot is looks like you've tried to open the object (to edit it in GDL) instead of opening the object's parameters (Ctrl+T or Cmd+T).
The standard practice for organising your objects is:
1. Default Library (what comes with your localised version of ArchiCAD)
2. Office Library (a folder where you keep other downloaded objects which you would use regularly)
3. Project Library (where you keep objects relevant to that particular project). Ever since embedding was made available, you have had the option to do so instead of having a project-specific library.
All these folders (or objects in the case of embedding) need to be loaded via the library manager.
To get better help on this forum, let your signature reflect your OS, hardware and version of ArchiCAD. It's part of your profile.
Cheers.