Chapter 4: Kinds
http://inform7.com/book/WI_4_1.html
§4.5. Kinds of value
http://inform7.com/book/WI_4_5.html
§4.10. Conditions of things
http://inform7.com/book/WI_4_10.html
§4.12. Values that vary
http://inform7.com/book/WI_4_12.html
You may also want to check out the Hybrid Choices extension if you want numbered menus at some point for selections in game.