It sounds as if, from the nature of your questions, that you have little/no experience with "gas welding?"

There should be a community college class locally dealing with welding, and specifically O/A. Never mind that it may not deal solely with "brazing." You have a bit to learn about heat control, torch control, and get the practice co-ordinating both hands, not to mention becoming familiar with the equipment.

I read the text in the link you provided. I wouldn't read any further until you get some hands-on. In fact I'd disregard that altogether. There's more than a few inaccuracies, and it may confuse the beginner. Whether it was the authors intrepretation of the subject, or he just plain didn't know I'm not sure. On the subject of Paterek- many feel this is not the best resource, me included. You might get something out of it if you have some experience, but there are better resources.

Over at the frame builders collective, Dave Kirk has a thread on "fillet brazing." Not a tutorial as such, but a good example of some excellent work. Again- you need some experience.

Supplies will be available from a welding supply house. Yellow Pages lists a few. They have an Airgas store there. That would be a good place to start.

Practice materials? At your level pretty much anything you can stick together. There's a lot to learn before attempting to stick bicycle tubing together. When you get to the point that you want to practice "bicycle joinery" use something approximating the tubing used in bisysle construction. I began wielding a torch (along with other weld methods) in dad's shop at maybe age 10. I'm about to turn 67 and been welding pretty much steady since. It was until about five years ago that I started f'brazing bicycle frames. I consider myself a pretty decent welder, and it wasn't like I needed to re-learn welding, but there are some considerations that are different. I wouldn't suggest anyone try to learn welding attempting to join bike frame tubes. You'll give both welding and bike building in a hurry..