Beer Gun Operation Instructions

I was psyched to get my beer gun, but only used it once since purchase - mostly because I've taken a small break from brewing and majority of what I have brewed went straight into the keg and draught. But I digress - The first time I used my beer gun I don't think I primed the bottles enough because when I tried the beer a few days later it definitely went bad (i.e. skunky and bad odor). Is there step-by-step instructions out there on the proper use of the gun? I want to start using my gun more and make sure that I use it correctly.
Thanks!