[Zope] Cataloging AND (indexing OR meta data)

I've got a bunch of objects that I catalog. I have added a few properties to the Indexes which makes it possible for me now to search on these properties. Everything is jolly! However, I honestly don't understand the Meta data tab. All I can practically do there is add names of properties and that already works spendid with the Indexes. Anybody got a clear explaination for ZCatalog-dummy on this one? PS. I read the Zope Book chapter on meta data but despite that I still didn't get it. Hopefully I've just lost a very important small piece of knowledge that is needed. Cheers, all