Metal roof flashing--best one?

[Mr Russ]

I have a metal roof similar in profile to this picture and i need to run a 3'' vent pipe thru it. Could someone recommend me a good roof flashing and a procedure on how to install it?

I found this one but im not sure how these things work and how to install them.
http://www.amazon.com/Oatey-14052-0-...ds=Oatey+14052