(1) Button Menu
It is a menu for displaying the scene list and asset list, as well as the publishing screen.
It is a list of all of the assets that have been placed. From here you can select an asset and then delete it, move it, rotate it, shrink it, etc.
(3) VR Start Position
This is the starting position for when you are viewing a scene in VR.
(4) Scene Gizmo
The scene gizmo indicates the direction the camera is currently facing. By clicking the red, green, or blue cones, you can quickly change the camera viewpoint to have the corresponding axis point forwards.
(5) Scene Control
These buttons perform different operations within the scene. For example, they can be used to move and rotate assets, as well as set the initial camera position.