Select the camera tool on the map tools bar. It's the third one down on the list and looks like a red 35 mm camera.

Holding the left mouse button while in the 3D view will allow you to look around from a stationary point. Holding the right mouse button will allow you to pan left, right, up, and down in the 3D space. Holding both left and right mouse buttons down together will allow you to move forward and backwards as well as pan left and right. Scrolling the mouse wheel will move the camera forward and backwards.

Practice flying down the example map hallway. While looking down the hallway, hold the right mouse button to rise up through the grate and see the top of the map.

If you would prefer another method of navigating in 3D, you can use the W, S, A, and D keys to move around while the left mouse button is pressed....