NEWBIE-Q : CAN I HAVE MY OWN DNS?

I know that it is possible but what I really want to know is can I host my own website on an always on computer with web+ftp+email server software AND also have a domain name server? , ultimately having my own website with all the webspace I could possibly need, ftp access, emails and a dot com domain name for absolutely **FREE**??? IS IT ACTUALLY POSSIBLE??? If so then OMG why are these silly companies selling webspace and domain names??? Wow I can finally have whatever content I like on my site and get away with it. Yippee!