Hello,
The chest is build up out of wood, which are seperated inside the chest object for example. Is there some rule of thumb, when to decide these should be seperate objects (in the outliner) en when should it be in one object? (hope i am stating this correctly.. )
There is no rule, but, as you will learn later in this course, here it is practical to make the wood planks seperate Objects (within a Collection, maybe called Chest), because you can make 'linked' copies of the planks (which you wouldn't be able to do if all the planks were parts of one Object!). This means that you can model 3 or 4 planks and build the whole chest with them ( You will see that in action later on).