Model Source Selection
After launching the sample, the user is prompted to choose a model source. There are currently two options for the model selection: Primitive and Prefab.

This determines which 3D model will be loaded into the scene for annotation and marker placement.
Primitive Source
When Primitive Source is selected additional option becomes available, here you can select a Primitive Type to be used as a model.

This primitive models are instantiated from built-in resources at runtime.

Prefab Source
Currently, Prefab Source references to one .glt model that is stored in the Sample, it could be replaced with any other compatible Prefab or GameObject reference in AttachmentsSample script
