Yes, view layers are covered in the compositing. I watched first. I know I should have started with modeling, but since that’s my second weakest area I’ve decided to do it and my weakest sculpting last.
1. If you select objects and press Ctrl+g you create a hidden collection (technically an unlinked collection). The collection is still part of the blend file along with all objects assigned to it. They just aren’t linked to the scene. Under the hood, this unlinks the collection from the scene and links it to a fake user. So the collection and all objects in the collection are then linked to the fake user. This is just like a material when you click the shield 🛡️ icon. Clicking that icon assigns the material to the fake user. That way if you delete the material (unlink the material) from the object it is still a part of the blend file.
2. First, object instance(linked duplicate) are object containers that share the same data. Mesh data in most cases. We refer to objects by their data. For example a light/lamp object is an object that has light/lamp data and yes lights can be linked duplicated. Second, collection is a container that holds collections and objects. When you instance a collection, you get everything that is in the collection, and it acts as one object. A good example of this is a school chair and desk. If you instance a collection with both in it then the chair and desk act as one object. So the objects become the data for the collection instances.
