New to modding

I would like to make a rappel mod, but i dont know how to select the player and the place where the player is standing for the two ends of the rope.
If someone could help me that would be great!

if your try to make a grppling hook kind of thing theres info just doing a google search i.e https://github.com/stujones11/shooter/blob/master/grapple.lua

Mine is more simple, i just dont know how to select.