How do disks generate lift?
As with regular wings, the angle of attack and the dynamic pressure determine the lift of a frisbee.

This short paper by V. Morrison gives a short overview. If you want to dig deeper, Sarah Hummel and Eugene Motoyama (sorry, paywalled) have done more detailed work on flying discs. The following pictures were shamelessly copied from the work of Kevin Walsh. They show that the rounded edge improves airflow over the disc by delaying flow separation.



Flow around a frisbee (source)

The frisbee can be seen as a wing with an airfoil that looks the same from both directions. This incurs a small separation area at the rear end, but prevents much larger separation at the leading edge at medium angles of attack. Morrison found the farthest flying distances with an angle of attack of 12° and a starting speed of 14 m/s.

Since the center of pressure is close to the leading edge, a disc would quickly topple over due to the different locations of the center of pressure and the center of gravity. By spinning, it can be stabilized:



Difference between spinning and non-spinning frisbee (source). Inertia / gyro forces prevents the spinning frisbee from pitching up.