To do a flip you need to activate the parameter "ACRO:Exponential agility boost". This boost the agility of tilting maneuvers.
Now get into the air and switch to ACRO mode. Start rising with full throttle than put the throttlestick down an turn the nick or roll stick quickly to the direction you want to flip.(Here the boost comes into play).
Wait until the flip is almost done. Nowthrottle up slowly and release the nick or roll stick. If everyting went fine you should hover again.
Tip: Try extreme pan/tilt maneuvers in ACRO and learn to catch the Shrediquette from extreme conditions without crashing it before you attempt your first flips.