This is a good place to start
So firstly there are 6 aux outputs that output 2 types of signaling, either "servo" or relay. Servo would be used when the device that you want to control uses PWM input and relay when it requires just 0/3.3 volt input. You can change this combination of servo/relay allocation of those 6 outputs with the parameter BRD_PWM_COUNT. Also consider these parms
SERVOx_FUNCTION where x is 9 to 14 for AUX 1 to 6 respectively. This parameter will determine what function is performed.
CHx_OPT where x is the channel number from the receiver. This will determine what function is performed when the PWM is above 1800.
I recall for my retractable landing gear that was connected to the first aux port I set these as follows.
CH9_OPT 29 (Channel 9 on the radio is mapped to a switch)