for rss feeds -
turn on rss feeds in my ebay
take the file they give you and copy it to your clipboard
go to feedburner and create an account and paste in what you copied from ebay
select an icon (or icons) to use and copy the code for it (them) to your listings. I also recommend in smaller text, under the icon, 'click here to subscribe to my RSS feed'
googlebase is totally different from rss feed. there's a couple of threads on here with info on googlebase.
hope that helps