Thread:Template talk:Extension/Can someone help me please

I think I have read every page about templates there is. I have search info from google about these Templates. Only topics about these templates I have found are people talking how confusing these are. I haven't found one step by step tutorial. Am I just too dumb?

My first question would be, why is there "copy and paste on top of your page" if that doesn't work :)

Even on this page there were that "create extension" and after that, foo. I have now wrote --> Template:Infobox4all in search.-->      (On my own wiki!) Create the page ---> I have copied everything from "view source" from this page. https://www.mediawiki.org/w/index.php?title=Template:Extension&action=edit

Now I get broken code with red-links. I have struggled with this for 4 days now. Do I need some Extension? Does somewhere on this page read what extensions would be needed. (I have parserfunctions btw.)

I would really appreciate if someone could help me with this. Please.