I want to read .frm and .ibd files in mysql to understand how mysql database engine store data in files. Which format those file does have, since when I open those files it show non-human readable characters.
Jeremy Cole in a series of posts explains InnoDB internals and on disk format in particular.
I'd start from https://blog.jcole.us/2013/01/02/on-learning-innodb-a-journey-to-the-core/ . Get his tool
innodb_ruby, it's very helpful in the learning.