Unable to use Port 80

Well, you've identified WebHop as the solution so you're most of the way there. The what is going wrong is covered here.

In summary, you need 2 hostnames. The first (realhost.example.com) is the one you update with your current IP. Once you've forwarded ports (as covered in the wiki) you'd access your web server using that hostname and port (for example, http://realhost.example.com:8080).

The second is the WebHop hostname (myhost.example.net) that people enter in their web browser so they don't have to know the port. This is configured with the URL people would otherwise have entered (http://realhost.example.com:8080).

If you need it explained further you'll have to say what you don't understand.

Cry Havoc, I am using free DynDNS service... When I select "WebHop Redirect" option, it asks me for "Redirect URL:" and I don't know what to type in there!

The URL which I have chosen is http://vinaya.selfip.com for my website. For this URL, should I use Webhop or my public IP address? And if its Webhop, what's the URL for it?

Linked from the WebHop service page is a tutorial that answers your questions.