spline twist and not match

I’m trying the video tutorial of “Using Splines and Spline Components”. but end up two problems. Please help!!

I made a simple Rope_Bp , check it out here

I have check your version of rope. same thing happen when rope goes up and down. but looks like your do better job.
Can you explain What does the last set of codes do? the “Get Ypvector at spline points”, “Normalize”, and “Set Spline Up Dir”.