The new navigation gadgets are a pretty big change from the previous versions of Google Earth. They are designed to help you realize the full potential of the 3D environment in Google Earth. Google has updated the Google Earth User Guide, and they have added the following video to help explain the new gadgets:
Here are some other tips for navigating:
Fast zoom – You can zoom in/out quickly by pressing the right mouse button and dragging up and down. NOTE: I find it annoying that the direction of motion is the opposite from the behavior of the zoom gadget (up is out, down is in for the mouse zoom).
CTRL arrow keys – you can move your view like with the “look around” gadget by pressing CTRL and using the arrow keys on your keyboard to move your view.
Middle Mouse Button – if you have a 3 button mouse, use your middle mouse button. Click and hold the middle button – you now get a marker for the place you clicked and you can hold the button down and use your mouse to tilt and rotate about that point. This is a little different than in previous versions of Google Earth, but it works quite well.
Reset your view – to get your self re-oriented quickly – click in the 3D window and then hit the “r” key on your keyboard. This resets to “straight-down, north-up” viewing.
New shortcuts – Here’s some other tips on shortcuts for navigating from the new user guide.
Also, read the official GE User Guide on navigation (as linked above).