When you place an Object (as opposed to other elements in Archicad), you are placing an instance of an external file located in an object library. Archicad is shipped with a standard object library containing hundreds of preconfigured, editable objects (also known as GDL objects or Library parts). For the most part, you will use Archicad tools to place objects from this standard library.
Objects are parametric. This means that you can freely configure the placed instance, using the Object Settings dialog box, or the dialog boxes associated with the object-type tools, without actually modifying the source file for the object.
See Settings of Library Part Elements and Object Tool Settings.
Where to Find Objects for Use in Archicad
2D and 3D Representation of Objects
Parameter Transfer Between Objects
Graphical Editing Using Editable Hotspots
Create Custom Library Parts and Components
Further Resources on GDL Object Creation