To make a feed visible on your Google Personalized home page, enter the url into the box located under the "create a section" header. If you don't know a feed's url or want Google Personalized to suggest feeds of possible interest, simply enter a feed's title or subject into the box.
Once a feed appears is added to your Google Personalized home page, only titles/headlines are visible. You'll need to click again to view the full text. It's also possible to change the number of headlines/titles visible (default is three) by clicking the edit button. Up to nine headlines/titles can be viewed on the page.
The Google Personalized Home Page went live in May. Here's Danny's overview article.
Another new Google Personalized feature offers an option to list important bookmarks on your page.
Postscript: I noted above that you could search for RSS content using the new feature, but it's worth stressing this significant change. The ability to search effectively gives Google a rudimentary feed discovery service, as Nathan points out, similar that offered by Yahoo and MSN Search, not to mention Ask Jeeves-owned Bloglines.
Postscript 2 (from Danny): After scratching my head wondering why the darn thing wasn't working for me, I came across Brad Hill's post that the CustomizeGoogle extension sadly is the problem. Sure enough, when I got rid of that, the page worked for me.