Changing the state on the iPad will power it up, but if you would like to start it on your own without using the EFB (from Cold and Dark cockpit), proper sequence would be:
Battery Master switch ON
APU PWR FUEL button ON (Left one)
Wait a few seconds and press the right one (START / STOP switch).
After 10 seconds or so the APU should be online.
Looks like you found the Vol3_Tutorial.PDF. Would highly recommend that for others that are learning the airplane.
