Part 1
This first part gives an overview of the process that will be used to miter the ends of the tubes, so that they fit neatly against the head tube, seat tube, and bottom bracket.
Part 2
This part focuses on the actual process of mitering. The outside surfaces of the non-cut tubes are copied (offset at 0mm) and used as cutting surfaces to trim away excess material from the tubes that will be cut. Then, using the "Cut with surface" command, the excess material is removed from the Top Tube, Down tube, Stays and seat tube.
Part 3
Part 3 continues the process started in Part 2. The down tube is mitered at the top tube and seat tube, and the bridges are mitered at the stays.
The last couple of seconds of this video are cut off. They merely explain that it is a good idea to delete any surfaces, at the end of mitering process.