Ok, so first of all i would recommend you to take a look at
http://forums.webhostdir.com/showthread.php?t=7957 (they have some usefull stuff there, maybe whrforums.com has something like this too, but i had the link above right next to me:))
As you have registered the domains, by now you should have the domain control panel (the one in which you can configure the name servers for the domain and so on).
So the next thing you do is Purchase a Hosting account. You choose a company (any that you like).
When you purchase the account they ask you what domain you would like to use for it (this is the main domain, with which the hosting is associated). Some companies offer free domains that they register for you free of charge, some don't. But this is not an issue for you as you have the domains already. So you specify which domain you would like to have as main for hosting.
Then the hosting company (after you have paid), sets up you account. Then, after the setup is complete they send you information (it is the IP address of the server your account is situated on, the username, and password and so on). Usually the management of hosting is done via special control panels like cPanel. You can search for it in Google to try the demo of it. The other thing they tell you is the name servers (domains and IPs – usually look like ns1.domain.com and xxx.xxx.xxx.xxx, where x are numbers). Name servers are the servers that contain information about where to look for the content of the domain yourdomain.com (i.e. on which server the content of this domain is hosted). So as soon as you get your information about your name server you go to your domain control panel and specify the name servers. Then wait for 24-72 hours (this is the time of DNS propagation – time during which all the internet gets to know where to look for content of yourdomain.com). As soon as the propagation is done – you can view your site in the browser and so on.
Ok tried to do my best to explain this stuff
Feel free to ask if you have more questions.