There’s actually a recommended quickstart guide for getting to grips with the Arduboy itself when it arrives.
(Note that Codebender isn’t used as much any more though, it’s lost favour with some people.)
There’s also an entire tag/category on this website dedicated to guides on how to do various things with the Arduboy: http://community.arduboy.com/c/arduboy/guides
And if you’re struggling with something or can’t find an existing post that solves your problem, you can always ask for help (remembering to provide a copy of the code causing the problem along with your explanation). Even though this is a website about the Arduboy specifically, you can still ask questions about the C++ language in general.
For learning about the Arduino board itself and the IDE you’ll probably be using (until you’re comfortable with it and are ready to try using other tools alongside it), the Arduino website has this page: https://www.arduino.cc/en/Tutorial/Foundations
Note that the information about the pins aren’t necissarily going to be useful to you in the early stages, but the Programming section and the part about the different types of memory available on Arduino boards are handy things you can read even before you have your Arduboy.
As for programming, your best place to look (assuming you have some programming knowledge already) is right here on the Arduboy forums. Most people put the source code for their games up on Github, where you can download it and read it. This won’t always be helpful if you don’t already have your Arduboy to try the code out on, but it provides an insight into how others choose to write their code and helps to illustrate some of the features of the Arduboy library (and the Arduboy2 library, an alternative).