New subscriber - looking for an overview of the code

Hello devs,

I am a coding enthusiast. I have downloaded code in a Ubuntu VMWare machine and I am able to compile the code.

I am looking for a course / site that can give me an overview of the code like:

1. How is the code organized and which file/folder has these components?

     * Core RDBMS engine components, 

     * additional DB components, 

     * DB Rule based security components  

     * DB Storage components

    * Index storage

2. Is there a code sample that can demonstrate DB engine changes (like a sample to change SELECT to SEL or SLCT, or adding a new mathematical operator)

Thanks