Depends on what you want to use the site for.
To start with :
.com - companies (usually American although not always so these days)
.net - companies whose business is mainly with the internet - e.g. ISPs
.org - non-profit making organisations - e.g. charities, PPRuNe
.co.uk / .co.de - companies in a specific country - uk, germany etc.
You won't be allowed a .net or a .org address unless you can prove you qualify for one.
There are lots of ways to get your own domain name -
www.freenetname.com is one who will give you one free. There are catches though, mostly involving advertising. Normally you would pay something around £50 to register it, then a nominal fee, say £25 a year to keep it.
Web hosting is where another company hosts your web page on their computer, rather than it sitting on yours. This is normally the way it's done, unless you are a large corp. with your own dedicated internet servers. You would usually get a fairly large chunk of diskspace (10Mb+) to put your pages on.
If you are serious about starting an e-business, it might pay to invest in a professional site designer. There are several tools on the market, some free, which are easy to use. The more powerful web design tools are a tad trickier and need knowledge of HTML. Microsoft's FrontPage 2000 is probably the easiest and most powerful of the off-the-shelf tools. Somewhere in the region of £200 to you.
If you were thinking of adding the latest multi-media to your site, purchasing Shockwave or Flash would put an even bigger dent in your wallet.
Collecting cash is hideously expensive with the 'no-business-history' credit card schemes which skim 10% off the top of every transaction.
If you just want to post pictures of your **** and leering mates at the pub, stick to your ISPs homepage package and use FrontPage Express which, again, is free !
Hope this helps
Cheers