creating subdomains on main domain

I'm working on a personal project where a person (not necessarily a user/ no authentication necessary) can go into a main web page (www.somesite.com) and do some 'stuff'. After said stuff is done, there is a save button somewhere on the page and a 'name' input box.

what I want to happen is, when a name is provided, and the save button is clicked, a new subdomain is created that looks something like this, and this new page will just have some info or details about the stuff he did:

http://ift.tt/1KPd3L8 <- doesn't have to be .html

what is this process called, it seems like 'subdomain' is not the right term for it, and I can't figure out what to search to find a tutorial or something