Hi Tarek,
We include the Argotic framework library for RSS in mojoPortal. The Argotic library hasn't been updated in a few years but it works well enough.
You can find example code in our blog feature (RSS.aspx) of how to use Argotic to generate a feed, and that can help you learn how to implement your own RSS feed. Argotic also supports Atom feeds and a few other things.
Hope that helps,
Joe