Refer to the Minimum Setup article of CKEditor 3.x Developer's Guide for a brief description of all files and folders from the CKEditor installation package as well as information on what can be safely removed before you upload CKEditor files to your production server.
How Do I Know Which Files I Can Remove Before Uploading CKEditor to My Server?
This website contains links to software which is either no longer maintained or will be supported only until the end of 2019 (CKFinder 2). For the latest documentation about current CKSource projects, including software like CKEditor 4/CKEditor 5, CKFinder 3, Cloud Services, Letters, Accessibility Checker, please visit the new documentation website.
If you look for an information about very old versions of CKEditor, FCKeditor and CKFinder check also the CKEditor forum, which was closed in 2015. If not, please head to StackOverflow for support.