If you want to learn programming in BYOND, your best first step is still the DM Guide. While it pertains to an older version, most of the advice and info in it is still perfectly sound, and it's a great place to start. I would also highly recommend Zilal's tutorials, which you can find in the developer section. Keep the a bookmark for the DM Reference handy for whenever you need to look up some info. And if you run into any issues, you can bring your specific questions to the Developer Help forum. Good luck!