Where do I start?
Are you wondering if you might be trans? Try this one first: That's Gender Dysphoria, FYI -- a comprehensive guide with information about gender, various ways dysphoria can manifest, different methods of handling it.
Another great resource: Gender Transition for Dummies, by Adrien Lawyer, Erik Wolf, T. Michael Trimm, and Molly McClain, MD.
Check this one out, too: Genderqueer Identity (GQI) Scale