(?) How would I... (domain question)

Okay, as a hypothetical situation, let's say I own boogle.com, and I want to purchase the domain called bmail.com. The name isn't so important... These names are just so people will have a better understanding of what I'm asking for...

Anyway, so I go to Registrar-X, and purchase bmail.com. My question is, how would I set it up so that you can either go to mail.boogle.com OR bmail.com and get to the same exact site with the same exact information?

Please be really specific with your response(s) pertaining to this entire process, because I'd like to set something like this up, starting tonight, if at all possible.
Thanks.

You mean a subdomain? Decide which one you want to use and then 301 redirect the other one to it.

Learn about subdomains, you didn't need "bmail.com", you could have used "mail.boogle.com" and call it "bmail"