Jim - Web pages are written in HTML (Hypertext Markup Language). Podcasts use a variant called XML (Extensible? Markup Language).

A podcast is an MP3 file which can be automatically downloaded by a special programme designed to do so.
The XML files used for podcasts give a Podcast Reading Programme the location of the MP3 file.
With a series of podcasts e.g. a weekly radio programme, they add a bit of code for the new MP3 file each week. This means thet the list of instructions gets longer over a period of time.

XML has a slightly different set of rules compared with HTML. It is not designed to make a page look fancy. You can view an XML page in a web browser, but it appears as a page of text. Usually the text would contain nested instructions with different lines inset so that the programmer writing the page can keep track of which instruction belongs where.

Here is a link to an XML page from weird band They Might Be Giants who do a podcast approximately every month. http://www.tmbg.com/_media/_pod/podcast.xml
I expect that is not a standard format as it appears to be designed for putting it through the Apple i-Tunes web site, but it gives an idea what one looks like.

A lot of computer stuff follows standard formats. The easiest way to make a web page is copy the code from somebody else's page, then delete their content and substitute your own. Same goes for XML. Find one that works and then use the same format but with the web addresses for your own files.
Quack!
GtD.