Help with explicit passing of blocks to each

[neidiom]

Your article 'How to learn Enumerable really really ridiculously good' and is great way to exercise Ruby but I failed on the first step with overriding each method. I played a bit here
https://github.com/neidiom/ruby_playground/blob/master/each.rb
but I think it would be great if you could write some pointers on this subject.