There are two ways to observe and manipulate your models: Orbit Mode and First Person Mode. You can switch between these modes from the Viewer Mode menu.
Orbit Mode
Orbit Mode allows you to rotate around the object's origin in three axes, similar to most 3D software.
First Person Mode
First Person Mode lets you "walk" in 3D space and look around, like you might see in a first-person video game.
If your graphics card is not webGL enabled the 3D model will default into an image-based fallback viewer, which emulates a true turntable-style viewer.