A little help please

I need your help please.

I am still learning my way around Raspberry PI so not always sure what to do.

I have Pixhack and RPI 3.

I have installed the ApSync image on my PI I just need a little help with getting it all working.

Setting up the Serials is the easy part and I have connected my TX RX to the GPIO pins.

The pi is powered Via the USB port and I have one negative lead connected to the GPIO pins as per the ApSync instructions.

Can any one tell me what I need to do next to get the telem to work over the GPIO pins and how to setup the UDP .

Thanks in advance.