I was hoping to make this the topic of my first ever video tutorial, but I still haven't got round to cleaning my desk of all the junk and setting up a holder for my phone to use as a camera. Plus I am suffering from a bad cold right now and sound awful. So text it is.
I'd like to help you get to know exactly what a digital IO pin of an Arduino actually is and how it works. Many questions I come across along the lines of "How does this work", or "Why do you need to do this", or similar, can be answered easily if you know exactly what goes on inside an IO pin.