how to use _source files

Hi, I am pulling my hair out over this.
I have no trouble installing ckeditor, and using the supplied ckeditor.js. The problem is that is too hard to read, so i thought it would be better to use the _souce/core files. How do i do this? How does it all fit together?
i have tried just swapping the ckeditor.js file from source to the base folder (ckeditor)
i have tried referencing the javascript like ckeditor/_source/core/ckeditor.js
what exactly is in the supplied ckeditor.js file? it is huge (kbs)
There also seems to be no replace function in the core/ckeditor.js

Any help would be appreciated.