For extra control in exploring the 3D environment, right click anwhere in the world and select the Show toolbars/Hide toolbars option. Obviously if the toolbar isn't already visible you would only see the "Show Toolbars" option and vice versa.

Once you select the "Show Toolbars" option you will see the navigation bottons (shown below). On the left you have:

Walk - allows you to click and drag to walk through the world
Fly - allows you to move in 3 dimensions: X, Y and Z (Z being up or down)
Study - Lets you rotate around a central point. This is mainly used for viewing single 3D objects.

Note: these options are not always available and "Walk" is the option commonly displayed.

The other options Plan, Pan, Turn and Roll change how your mouse interacts with the world. For example "Turn" lets your mouse move your viewpoint asthough it were a possible head (up and down etc.)

The options at the bottom work as follows:

Align - This is useful if you've moved your view to a strange angle and want to re-align it.
View - There may be several cameras in the scene. Click here to change between them.
Restore - This is used to restore your view to the starting point again.
Fit - Use this option for viewing individual products that utilise the "Study" view.