3D isn't called 3D just because it's a catchy name — the name refers to the three-dimensional space that 3D objects occupy. In this space, coordinates along x-, y-, and z-axes represent an object's position. The center or origin of the coordinate system is located at x, y, and z values of 0, 0, 0. What all of this means is that you can view the object from any angle by positioning the 3D camera in space relative to the object.
This might all sound fairly complex, but the good news is that Photoshop offers a 3D View tool that allows you to move the camera in a multitude of ways relative to the object in the scene. Figure 27.4 shows the various iterations of the View tool, which are all grouped together in the Toolbox.
These additional modes are also available in the Options Bar whenever any of the camera manipulation tools is active. To use the 3D View tools, first select a 3D layer in the Layers panel, and then click on one of the tools, or press the N key. You'll notice that when you select one of these tools and hover over the canvas, your cursor changes to give you a visual indication of what the current tool actually does.
If the currently selected layer isn't a 3D layer, you'll see the familiar "oh-no-you-don't" circle with a line through it when you hover your cursor over the canvas. Select a 3D layer and you'll be good to go.