QR Codes: What's this and How it Works

Sometimes when you buy something, you'll find a logo on the box with black squares, or you can find it on some websites online, on ads boards in the street.. it's everywhere, these codes are called QR Codes.
But do you never ask, what are these codes, and how it work?.

The QR codes (or Quick Response codes) are designed especially to attract peoples attention, these codes are everywhere and we can say that it's a kind of link (or text) shorting.
So in one sentence "QR codes are Matrix bar codes to Store Data", these codes appear for the first time by Denso Wave as a new way to attract cars (vehicles in general) during manufacture. But now they're more than this:

QR codes may be used to display text to the user, to add a vCard contact to the user's device, to open a Uniform Resource Identifier (URI), or to compose an e-mail or text message. Via Wikipedia

For example if you scan the QR code in the top of this post, you'll be redirected to Netisia home page, you can use goqr or Scanova to create your own qr code and you can scan the code with one of QR codes apps on app store or google play (just search qr code).

OK, I think you know what are these codes and when you see it in the street you know that it contain a link or other information in it (just scan it with your smartphone to discover), and it can hold 100 times more than 1-D bar Codes
But the question now is, how these QR codes work and how smartphone camera can read it?.

In the reality these squares are a kind of messages, like coding languages or any normal language, it's created to be easy for computer and hard to peoples, why?, to attract their attention.

this is how QR codes work

As you can see, it's very complex and hard to understand (that's why it's created for computers), but I will give you a small and easy idea.
The photo here show you that every letter has an equation: 62+16+2=82='R' and it's the same thing for the other letters.

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