> Hello, I don't understand how to copy a mobile
> version of a website. I understand that I need to
> change Browser ID but I don't really understand what
> to change.

The browser identity can be changed to a mobile browser string ; such as:

Mozilla/5.0 (Linux; Android 4.4.2; Nexus 5 Build/KOT49H) AppleWebKit/537.36
(KHTML, like Gecko) Chrome/34.0.1847.114 Mobile Safari/537.36

See other example:
<http://id.furud.net/showdb.php?page=0&fake=31333&filter=mobile>