What ppm to to apm2.72 to control a quadcopter,

Dear sir or madam,
I want to send ppm from arduino uno to apm2.72 to control a quadcopter, but I failed to know the format of ppm. For example, what format of ppm should I send if I want to make the quadcopter fly forward? Please also tell me the ppm format of other functions.
Thank you for your time.