In the 3D Viewer, you can see all the objects in your scene. It shows the real-time results as you make adjustments to the scene or each of the objects. It also shows the focusing status of objects as you pick them in the Scene Tree. The viewer can be normal or full screen mode.
You can change the camera view in the full screen mode to observe the scene in different perspectives:
Zoom In / Out - Press down both left and right mouse buttons, move the cursor up / down to zoom in / out.
Horizontal Roll - Press down the left or right mouse button, move the cursor left / right to roll the scene horizontally.
Vertical Roll - Press down the left or right mouse button, move the cursor up / down to roll the scene vertically.