Oh boy, I like explaining things!
Ok, now how to put it... Your zoom tube is gonna be a sequence of points, defined by the Zoom Tube Waypoint object. Your first point will have an angle of 0 (for the first zoom tube) and each point needs to increase the angle by one. Now, in front of the first point, make a sector about 64 units thick, with a sector type of Zoom Tube Start, and give it an unused tag.
Now, make a new sector outside the map. The only thing you're looking for is the top linedef. Make it face straight to wither the left or the right, and give it a length determined by the speed (most use a length of 256). Give it a type of Zoom Tube Parameters, and give it the same tag you gave the Zoom Tube Start sector.
Now, if you want to be able to go back through the zoom tube, make a sector right behind the last point, and give it the same tag as the Zoom Tube Start sector, and give it a type of Zoom Tube End.
...If you can't understand that, I don't know what to tell you.