Can anyone give me an idiots guide to the Twist Grip please? I've got a ballbearing, a spring, 2 pieces of metal and no idea whats going on with em. I've tried to make sense of a pic i found on this site but i cant see that its clear enough

Blimey mate. If youre using the one that came with the bike, forget it as I ground bits out to make it work for 5 speed.
If its another one cool, Theres a hollow section on the lower half where the spring and bearing fit, spring 1st. Theres a dark colour bit of steel with a cut out in it that locates on the bottom half also, I cant remember what the other bit does without seeing it and its too dark to go rummaging in my shed now!