According to Wikipedia, A QR code (short for Quick Response) is a specific matrix barcode (or two-dimensional code). The code consists of black modules arranged in a square pattern on a white background. The information encoded can be text, URL or other data.
1. Create QR Code: qrencode is an utility in Ubuntu used to create QR code. To install it Ubuntu open terminal (Ctrl + Alt + t) and type the following command
$ sudo apt-get install qrencode
How to make QR code
To create QR code write the following command in terminal
$ qrencode -o lovelinux.png 'I love linux'
Note: You can type qrencode --help in terminal for more options.