Hi Tim, pretty basic. Ours runs from the end of the boom to the top of the mast through a sheave and down to the bottom of the mast. I changed ours so that I can tension or ease from the end of the boom leaving the bitter end at the bottom of the mast tied off on a mast cleat.
The main purpose is to raise the boom up when not under sail. It has no useful purpose in trimming the main. Ours is 3/8 inch double braid from end to end.