The Wikipedia page does a good enough job. It shouldn't take more than 1-3 pages, it's a fairly simple concept.

https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form#Examp...

I stumbled into compilers by accidentally buying the Dragon book as a teen. BNF part I got through fairly quickly.

Jack Crenshaw's "Let's Build a Compiler" [1], starting from Part 2.

[1]: http://compilers.iecc.com/crenshaw/