What is the part of a URL before the domain name called?

So I have 2 questions:

1. What is this part called? en.wikipedia.org, the part before the domain name.

2. I wanted to make something like that for my website, like firstName.lastName.web For my personal page on my family web site.

   How do I do that? I know that if I just put a folder in the root folder, its treated as a /. Like so: lastName.web/firstName.HTML. That's fine, but not what I wanted.