The information is located in your user manual for the H520. You can also do a search in the H520 Help part of the forum. A simple google search will bring up the user manual that shows it as well. After reading your post, I would suggest for your own safety, and that of others on the ground, it would be advisable for you to read the entire user manual before flying to familiarize yourself with the H520 and it's controls. These crafts can be very dangerous in the hands of a person that is not aware of what it can and can not do.
Manual mode is for flying without GPS, GPS is the way you get your altitude via the triangulation between the orbiting satellites,,your Aircraft , the controller.& barometer.