There are two kinds of "tags": for one there are XML tags like <item>, and secondly people call key words associated with other media "tags", although the word "label" would be more descriptive.

Which one do you mean?

RSS standardizes which XML tags to use, so if you use an RSS parser, you don't have to worry about different XML tags on different sites.

If different sites use different labels, there is no general mapping from one to the other, but maybe in some specific case you can find rules for it.

Can anybody suggest how should i proceed...!!!

Start your work, write a script that downloads and parses the RSS. If you encounter a concrete problem, come back to us, and show us example data.