To film your flight, press ALT + R keys
You will notice a small letter "R" that will be red in the upper left hand corner of your screen.
To stop filming, you must press ALT + R keys again, or someone needs to kill you and send you to the tower.
Go to your aces high folder on your computer and open up your film with AH film viewer.
All your films are numbered automatically for you and saved in your "films" folder inside of your HTC folder on your hard drive.
For more information, go to the help files on this website.