Step 1 - buy a domain name ( ie.
www.mysite.com) .. for trial you can get a free domain name from this site -
http://www.co.cc/ , but only ***.co.cc names can be acquired for free.
Step 2 - Search for a good web Hosting site (ie. for free hosting website you can use X10hosting.com and others ), once you have registered, they 'll give you the hosting IP address. while registering you 'll automatically get the idea, where and what to fill. Now if you go to the file manager from your account, you 'll see a folder created(most of the time) with your domain name that you have given while registering. Now you can put the Index.html or other pages in that folder.
step 3 - Now as I said once you have registered in hosting site, you get the IP address, Now once again you need to go to co.cc acount ( or from where ever you have got the domain) their you need to give the ip address in the field "name server".
So you see that process will be like this -
Once somebody clicks your sites link (domain name that you have bought), it gets the hosting address info from the nameserver, since you have given the IP address of the hosting site in the nameserver, it automatically gets the pages from that hosting sites.
Since you can build your own website for free, so better way is to try it by yourself, if you have any problem then you can post it here.

, first time when i tried, i got to see my first webpage in 2 hours. ( though i'm not interested in these things, just wanted to see how it works )