Multiple Scenes can be combined to create more complex scenes.

To create the level combine the Background and Level Scenes.

Create a New Scene with a Node2D as the root.

Rename the Node2D to Level_1

Drag and drop the Background.tscn file onto the Level_1 Node

Drag and drop the Level.tscn file onto the Level_1 Node.

By dragging and dropping scenes this way we can create more complex scenes.

Your scene should look similar to this: