Known World Handbook
The Known World Handbook is a valuable resource to newcomers to the SCA. It is available from the Stock Clerk at: https://secure.sca.org/cgi-bin/stockclerk under other SCA publications. It is also often available from some merchants at events.
The handbook contains many short introductory articles on a wide variety of topics, and has set many a person on the right path. However, some of the articles are inadequate relative to current knowledge - it's a good idea to consult other resources as well.