God i'm confused
Let me get this straight, you only want to fill your gun bottle and not purchase a dive bottle?
If that's correct then you will need a din fill rig as pictured on other peoples posts, but you will not be able to hook that up to a compressor as the din fitting will be wrong on the compressor feed.....(it will also be a female fitting and two female fittings cannot be joined without a male/male adaptor and it's starting to get complicated now).................................................................
but if you have a friendly dive shop they will fill your bottle off of a pre-charged dive tank.
But go and ask at your dive shop first, as i have found them to be very reserved about their offers of help on anything non-fishy.
After all if you blow yourself up, the first question that's asked is who filled the tank and how?
Try going to another site, and getting a walk on player to demonstrate the fill technique, where in the country are you?
P.s if you look at the square rig on ascutt's post you'll see it has a small silver end on the left hand side, you should just be able to see an arrow on a ring (far left), this ring is the bit that is slid back when you push the rig onto your gun bottle, once it's on you realease the ring and it locks into posistion, removal is just a reversal of all that once the pressure has been vented.
From the questions you've asked i'm guessing your new to all this, so my advice is try and find some experienced players in your area to run through it, air tanks run at high pressures and are quite capable of killing you if you blow one up by doing something silly, but used correctly they are perfectly safe !