James its a tool for aligning the optics in your scope to ensure you get the best results.
A newtonian reflector such as the GSO dob will require periodic alignment ( collimation) to get the best out of it. You will need a cheshire (dont buy a laser) to keep the scope giving the best views possible.
Have a read of this
http://skyandtelescope.com/printable...rticle_790.asp
There have also been a few recent threads on collimation and cheshire eyepieces, the forums search function will find them for you.