BRL,
read on here recently that you can pick one up for as little as £19 for two years
You should be able to get them cheaper than that, however, you should check in the Small Print for the charges/conditions they impose in the event that you want to move your domain elsewhere. Reputable companies won't even charge -- others do, and sometimes take ages to process the request. An absolute nightmare if you aren'ta happy with the service your're getting, for some reson.
As to how you upload, that very much depends on what "facilities" the service provider gives you. At the most basic, you will get something called "FTP" (File Transfer Protocol [sic]), a clunkly command line version of which comes built-in to Windows. You can pick up a
much better FTP client off the 'net, if that's all your SP provides.
Your hosting company may also provide webforms which will allow you to upload stuff into the appropriate place. It varies quite a lot from provier to provider, but they should give you clear-ish instructions
Get back to me if you need any more help.
[ Hehe, my post and EC's crossed
]