Stone Butch means slightly different things to different people. (Just like all labels.) But generally stone butch is defined as a woman who is very masculine in appearance and sometimes (but not always) identifies more as a man than a woman. Some stone butches refer to themselves with male pronouns, some are comfortable identifying as female but still relate more to male interests and mindsets. Sexually, Stone Butch generally means someone who gets pleasure from giving not receiving. Every individuals boundaries are unique and the most important thing you can do in any relationship (but especially in a relationship with a stone butch) is to establish what they are comfortable with.
If you'd like to discuss dating a stone butch in more detail, I'd be happy to talk with you privately. I'm in a wonderful relationship with a woman who usually identifies as stone butch, and I know I had a lot of questions in the beginning. You can email me through my profile if you'd like more detailed answers to the questions you asked here or any other questions.
Good luck!