In my experience, Omer spearguns don't come rigged (but RA railguns come very well rigged).
We have just the thread for you:
http://forums.deeperblue.com/threads/dummies-guide-to-rigging-a-speargun.64504/
Personally, for your speargun, I would get an Omer rubber-bone style shock-absorber (muzzle "bungee") but other options would work fine too - you'll likely need to buy that (they sell them in 1s and packs of 5 - often overpriced
). Your speargun might come with some suitable Omer black braid for wrapping this, mine did. For the spearline, Omer black monofilament works pretty well (~1.6mm diameter?) and some aluminium crimps - mine came with those. Do one loop at a time: loosely fit the crimp then mushroom the end of the line with a lighter/match, then crimp, then glue. You don't need a special tool (but go for bi-cusped if you do), they are soft & easy to crimp with pliers. Crimp only across the flat wide (doubled part). Superglue afterwards.
You can make do without the bungee (if you need to wait for delivery) by using a length of braid & use sheet-bend or double sheet bend to attach the braid to the monofilament spearline (which has a small amount of stretch with should help - bungees are better tho').
The loop at the end of the spear has to be sized and positioned carefully to avoid getting in the way - take some time to make a good job of this. The line then goes up the side or top of the spear, through the muzzle, back down to the line-release near the handle, then back up to its attachement at the muzzle (ideally a bungee but alternatively braid, eitherway a clip or sheet-bend/double sheet-bend can be used to join them). In theory, sheet bends work, I just don't trust them so always use a double-sheet bend or swivel clip (heavy duty angling gear).
BTW My Omers had a small wire guide loop on the front - for use with a reel. I carefully removed those & put them in a safe place. Which model did you get? Can you post an image or link to an existing googled image? Some of the Omers have fancy muzzles which might offer multiple configuration options.