After some years of experimenting with Arduino, I decided that the time has come to share the knowledge I've acquired. So I here it goes, a guide to Arduino, with the bare basics for beginners and some more advanced explanations for people who are somewhat more familiar with electronics.
Every step will consist of a detailed explanation, then a summary, followed by a more advanced approach.
If you're a complete beginner, I recommend reading the explanation first, and then the summary. There will (almost certainly) be some parts of the explanation you don't understand. Don't worry, it is absolutely normal, it will become clear after reading some other examples in the next steps, just don't get discouraged!
I'll provide some links to the Arduino reference page, Wikipedia, and some other interesting sources. If you want to know more about about a certain subject, these are great places to start. Again, if you don't understand a word of those links, don't worry, it is absolutely not necessary for this Instructable, and especially for beginners, they can be very confusing or even demotivating. If that's the case, it might be better to skip them for now. But don't give up!
Although a tutorial like this might be very helpful, you'll learn mostly by experimenting yourself. Use this Instructable as a starting point, as a reference, but make your own projects, modify the given examples, try new things, search the internet, the possibilities are pretty much endless!