jumper  Connect your RC receiver “S” (signal) pins to the “S” pins on Inputs of APM, using the  jumper cablet hat came with your APM:Copter kit.  You must connect at least channels 1 ~ 5.  Channels 6 ~ 8 are optional. Your RC receiver will require power. Normally this is done by using one 2 or 3 wire connector between the APM Inputs and one channel output on the receiver. See  APM Power Details for limitations and important warnings.
APM 2.55 RC IN
If you are using a  PPM, put a jumper on the “S” inputs of channel 2 and 3, and connect the PPM input to channel 1. 
If you need to rearrange the channel order when using PPM and are unable to do this from the transmitter, you can do this with the RCMAP Advanced parameters. Read more about them here.
From: http://copter.ardupilot.com/wiki/connecting-your-rc-input-and-motors/