Hi Ben,
Perhaps if you told us where you are in the country, somebody could either suggest a club to visit or be able to meet with you to provide advice. It would be a lot easier and quicker to do that than trying to describe everything.
In respect of the gaff - half way up the gaff should be a metal band with a loop in it - thread your main halyard through that and tie it off. The main halyard then goes through the pulley near the top of the mast - with the halyard going from stern to bow. With the gaff jaws against the mast you should now be able to pull the gaff up the mast.
With the gaff back at boat level thread the main sail from bottom to top up the slot in the gaff - tie the sail off at the top of the gaff through the holes ( or treat yourself to a shackle and have that permanently tied to the top of the gaff). You should now be able to start hauling the gaff up the mast - stop when the jaws are at head height so that you can attach the piece of elastic or tie a piece of rope between the two holes in the gaff jaws. Haul the sail about half way up and start doing the lacing down the front of the sail around the mast. Haul the sail to the top of the mast and secure the halyard ( I tie a loop in the free end of the halyard so that if it comes loose from the cleat the gaff doesn't come crashing down on me) finish of the lacing, attach your down haul and out haul.
You should now have the main sail up.
HTH
Andy J
