Mirror (proxy) of the site, how to do it and where to start?

Question

proxy

Good afternoon, forum users!

There is a site - domain.ru ("acquaintances" with logins and passwords).
You need to make a mirror of this site manually. There is no access to the admin panel "domen.ru", that is, it is necessary:

​​So that info from domen.ru comes to moydomen.ru and in identity shows info from the main site. The task for me is the first in my life, so I need help, tell me at least where to dig, or I won’t refuse help either;)