I purchased a domain name for my website but the files are hosted some other place. The domain registration website show four name servers addresses. What are these. Can I forward my domain to a specific url by modifying these name servers.
The DNS servers (domain name servers) are the directories that know what your domains are pointing at. To point your domain to your website you need to change the records inside the DNS. Probably you want to change the A record named @ to point at your website ip address, and then have www point at @.
Some registrars will offer some kind of web interface to do this. If yours don't, and you still can change the name servers themselves, you may want to change it to point at one who does.
The name servers tell the domain where the files are hosted basically. Go to where the files are hosted and get the name servers for the host and then add those to the name servers for the domain (you will enter these where you bought the domain). After that you need to add the domain into your hosting account (usually can be done in your cpanel). When this is done it can take up to 24 hours for this to work (although it does not normally take more than 1 min). If you are still not able to see your site after this it's probably because your browser cache needs to be cleared.