OK, here you go. Not quite the laser you will have, but it gives you the idea:-
http://www.kendrickastro.com/astro/p...ollimation.pdf
Also, since you are buying the 2x barlow, you can also use the "barlowed laser" technique described there as well. Use it unbarlowed first, then put the barlow in and see whether it needs tweaking a bit more.
With that GSO laser, be sure the screw is well off the on/off switch when you put it away. Laser collimators are less than optimal with dead batteries!
But before you laser anything, do a bit of visual inspection through the focusser to check the secondary mirror is correctly positioned. Have a look at what Andy does:-
http://www.andysshotglass.com/articles.html (search around for the video on collimating newtonian telescopes)