Lab- Welcome Aboard; great lead question!
Juro- Kudos! - great place to focus this kind of info in.
Lab re-read this; taken from flydoc's post:
"The diameter of the end section (tippet or end of leader) you use depends on the size of the fly you want to cast, often gauged by hook size of the fly (the larger the number, the smaller the hook)."
So, translated (and I'm sure you already recognize this), your tapered leader finishes or ends at the 4X point.
You'll find a ton of good knot info in the Internet, which will identify instructional websites as well as cool books and where to get them- so, go have a look around and enjoy the tour!