What is the right usage of it? and when? dynamic, static, microstretching, pnf etc. When should each one be used?
Only do static stretching after you are warm, never with cold muscles, and dont do too much static stretching before your workout. You can do dynamic stretches as part of your warm up.
You should try searching through the forums here, there is lots of information on stretching.
The GPP dvd also goes over all of your questions as well.
as you might imagine, dynamic and pnf stretching can be done when the body is very warmed up and limber 
find your ROM in warm up, expand it in the cool down, how you do that is a matter of preference and ability. For excample, some tolarate pnf, but some dont etc. Do static streches after a light warm up, not forcing them and keeping them short (especially if its cold), then after properly warming up, do pnf and/or balistic, again pay attention to pain, balistic and pnf can really agrevate problems