How to add a node to a taxonomy term?
You need to add a 'Term reference' field on the relevant content type:


Go to http://mysite.com/admin/structure/types/manage/page/fields (where 'page' is the name of your content type).
Add a new field, using 'Term reference' as the field type.
On the next page, choose the vocabulary you want the content type to reference.
On the page after that, choose specific settings for the field.


Next time you go to add/edit a node of that content type, you'll be able to choose terms from your selected vocabulary.