Rotation, Zoom, and Focus in 3D Viewport
By default, the 3D viewport is focused on the center of the grid. You can rotate and zoom to view other parts of the design. You may also change the focus of the view by selecting an object or by panning the view.
For the most versatility in 3D turn ON “Select Objects From Any Stage” in the Panel.
Mouse Controls
Rotation: Click and hold the left mouse button, move the mouse to rotate from left to right.
Zoom: Click and hold the right mouse button, move the mouse to zoom in and out.
Pan: Click and hold the center mouse wheel, move the mouse to pan your view left to right. You may also use the Pan tool located in the tool bar at the top of the 3D viewport.
Changing Focus
Double-click on a landscaping item in the viewport with the left mouse button. The selected landscaping item will be highlighted in red, and your view will be focused on that object.
You also have the option of double-clicking the ground to focus on a certain area.
To focus on the center of the grid, left-click once on the Reset button at the top of the Viewport. 
Focusing on Multiple Objects: Single-click each object while holding the Ctrl key. Or use the selection marquee by holding down the Shift key, the left mouse button, and dragging the mouse to form a box around the objects you want to select.
For more information see Editing the Objects.