I think some clarification may help here. (Bob, I read the questions slightly differently...)
When you're working in Layout Templates, as Bob says, you want to import a collection to help visualize what you're designing.
You can save the template anytime.
The Close button can deliver two experiences, depending on the collection that you import.
- If you import a collection that does not use this template you get the option to apply the Layout Template to the imported collection.
- This is always the case when you create a new Layout Template.
- If you are editing a template that's already used on a collection, you don't need to apply it since it's already applied.
- When you edit an existing template, the import command prioritizes the collections for import. Collections that use the template are at the top of the list.
Yes, when you edit a Layout Template you need to choose which collection to import because you might want to try a different design. (You can switch the imported collection in the Mapping view of Layout Templates.)
Now to your screenshot:
The message at the bottom of that menu says that the Tablet rendition is the default that will be used if you now add a phone rendition.
You cannot set a default orientation for use in Layout Templates.
That command/option does not set the orientation for any collection, orientation is an app level setting.
HTH