Open Google Earth and press Ctrl+Alt+A on your PC or Command+Option+A on your Mac and presto, you are taken to Google Flight Simulator. Then all you need to do to take off is press the page up button and then arrow yourself higher with your arrow keys.
Once you are in the air, you can then play with the other controls and fly around.
Here is a video of someone flying around:
I admit it, I crashed a few times before I got the hang of it.