creating subdomains?

[ruttiger]

anyone know how to create a subdomain? I've always just asked my server guy to do it, but now that i got my own server with root privs, i wonder if there's a file somewhere on the server that takes care of this? I really have no clue here, and exhausted from coming this far with sendmail. I'd really like all subdomains of my domain to come to my server, and let my server accept them, then process where the email came from.

also, where are MX records stored and modified?
can i change these on my own?

thanks in advance,
Blake