Adjust track, line from corners

I’m trying to figure out the adjustment tool. The videos are of little help. Is there a guild to what each item in the adjust track tab does? What are the lines that exent out from the corners? Should I be adjust those or the corners? Why are the points moving after I set them?

Adjust Track can be difficult to get a handle on. Generally you set a master frame for each corner and then scrub through to see how the master frame compares to the current frame. You can adjust each corner to correct for drift and the new keyframes will interpolate on top of your original surface track.

When the corners are completely occluded or not visibile, you can use the New Ref button to create a new reference master and set this on a pattern or detail that is on the same plane as that corner. This is a way to do visiual adjustments on the corner when it is not visibale. The will only work on smaller areas that are relative to the vorner and the lines will change color - green is an acceptable offset, red not good.

You may want to read the user manual about Adjust Track here for more detail: Boris FX | Mocha® 2020 User Guide

hope this helps.