bootstrap your emacs lisp learning

So every now and then there's someone asking in /r/emacs about learning elisp. And I always answer with the same solution that I'm now posting here to avoid copypasting the whole thing every time.

In an attempt to give bootstrapped solution, t-shirt sized, and that is both a fish,  a fishing lesson and a fishing rod, this is what I came with.
 

• Type c-h k c-h k and read.
• Type c-h k c-h f and read.
• With the previous tools, try to understand the following:
  

  (defun foo ()
    (interactive)
    (save-excursion
      (beginning-of-line)
      (insert ";")))
  
  (global-set-key (kbd "C-c ;") 'foo)
  

• Select the whole snippet and type m-x eval-region.
• Type c-c ; .
• Try to understand what just happened.