The one thing you have to remember is you cannot own a domain name.
You register it for x number of years and pay the registry fee. Nominet and a few other companies are the main registars i think (i am not too sure).
The deal is you get the .com, the registar will then have information on 2 name serves. A main one and a back-up, although only one is needed 2 is prefered. These then direct the user to the server space where your website is.
You can get .tk for free, but that is casue they are a small country and like the advertising. I think there are ads here, but not too sure.
Renewals have to be payed to the regsitar every 2 years for a .com, 1 year for .co.uk etc. It depends on how inportant they are .coms are top and things go down from there. BASICLY.
.info, .tv, .biz, etc can cost more.
If you get a free domain with your hosting in reality you are paying for the domain with the hosting. Domains can be got for as little as $5 a year if you own the nameservers i think...
The Outside is a evil place to be, too much light, too much noise and too many distractions....
I went outside once and my FPS rate dropped to 5.