How to add pages to a website with the page name at the front

How to add pages to a website with the page name at the front

The title is probably confusing. Sorry.
Anyways, I finally got my website up and running at www.ersherm.com, but I
need to add a page for myself.
Now, I've seen websites with addresses like "page.domain.com" - with the
page name before the domain name. I want to make a page for myself with
the address "www.andex.ersherm.com".
Maybe I'm mislead, maybe that's not possible- I don't know that much about
this- but if it is possible, could somebody tell me how to do that?
Thanks.
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[-AndeX]