TinyWM is a tiny window manager that I created as an exercise in minimalism. It is also maybe helpful in learning some of the very basics of creating a window manager. It is only around 50 lines of C. There is also a Python version using python-xlib.

Programming in Lua provides a solid base to any programmer who wants to use Lua. It covers all aspects of Lua—from the basics to its API with C. The book is the main source of programming patterns for Lua, with numerous code examples that help the reader to make the most of Lua's flexibility and powerful mechanisms. The book is targeted at people with some programming background, but it does not assume any prior knowledge about Lua or other scripting languages.

learn-c.org is a free interactive C tutorial for people who want to learn C, fast.

everything you ever wanted to know about terminals

Learn C Programming Language basics in just a few hours