This document introduces free and open source software. It discusses how many commonly used programs like Firefox, VLC media player, OpenOffice, Android, Notepad++, 7-Zip, WordPress, and Pidgin are free and open source. The history of free and open source software is summarized, including Richard Stallman founding the FSF in 1985 and Linus Torvalds releasing the Linux kernel in 1990. Some benefits of learning free and open source software like better job opportunities and knowledge are mentioned. The document recommends resources like the Linux Documentation Project and distribution websites for help and highlights other non-coding ways to contribute like localization, documentation, artwork, bug reporting and mentoring.