How to categorize references in endnote 9 within a single library

I can’t seem to figure out how to do this, although it seems like I should be able to. Can someone point me in the right direction? Can’t seem to find anything in the manual



What’s your definition of “categorize”? 

I use specific keywords (before the groups appeared in X1) and used subject or just searched.  I would do searches to find the different variants of a topic in title/abstract and then use the Change or Move Fields option (I think it is under Tools), to globally add a word to Keywords or another field of your choice.