One shouldn't teach what one doesn't know.
Don't exepect to learn anything. This tutorial doesn't explain the actionscript properly, the author even admits that his understanding of the code he's teaching is poor. This makes the tutorial a poor aid, and frustrating when things don't work. I followed it to the letter and couldn't get the item code working at all, however at least the collision code worked to a degree. There are obviously much better ways to code a platformer though.