Easy-ish custom sub domain

Hey guys so not that I particularly want to do this, as I assume it would't be easy but I would like to know what the process and requirements are to create a sub domain such as "Google.skynet.com"
Would you need a custom DNS server, etc?

If you own the skynet.com domain you can create whatever subdomains you like. You can set up the subdomain on whatever dns server you're using, you don't have to run your own.

If you do set up your own dns server you will still need to register a domain name, but you can set up as many subdomains as you like (or how many your dns service will let you have)

ah ok thanks, alot. I will delve abit more into this, quite curious about to what extent someone could take it. Thanks.