[Trisquel-users] Share your favorite learning. resources

[albertoefg]

What books, ebooks, pdfs, websites, videos, tutorials, etc., do you like and  
are useful to learn about free software, programming, or using a program?

Currently I am reading "An Introduction to Programming in Emacs Lisp"
https://www.gnu.org/software/emacs/manual/html_mono/eintr.html
It is well explained, easy, and for begginers :)

So what do you suggest?