If you're talking about the rear takedown pin,the plunger is put in the hole first,then the spring and the grip then holds all of that in place. It doesn't go in from the rear like an AR15.
I am, but on this lower the spring and detent go in the right hand hole for the takedown pin. The spring goes down in the hole and then it looks like I need to put the buffer on top of that. Then hold it down in there far and lond enough to push the pin over it. I just can't figure out how to get the buffer to stay in there long enough to start the pin through.