Your text is encoded into binary data using a mode (numeric, alphanumeric, byte, or kanji).

Error correction codewords (Reed-Solomon) are added. Higher ECL = more of the QR can be torn/covered and still scan.

Data is laid out in a square grid of black & white modules. Finder patterns (the three big squares) let scanners locate and orient the code.

A masking pattern is applied to balance dark/light modules — prevents scanner confusion from large solid areas.