Question about taxonomy, tagging and existing nodes

I have another question in the post I made about the Tagadelic module, but now i have a more general question about taxonomy and existing nodes. When I view the "page" content type or any other type and I click "manage fields", I see Taxonomy at the top along with Title, both of which are not configurable. However, when I create one of my content types, either the standard "page" type or one of my custom content types, I do not have the option of entering the taxonomy for it. Is this something that happens automatically?