This website contains links to software which is either no longer maintained or will be supported only until the end of 2019 (CKFinder 2).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.
Use the dedicated CKEditor for WordPress plugin that is available on its official website: http://wordpress.org/extend/plugins/ckeditor-for-wordpress/.
Download the plugin, unpack it, and upload to the /wp-content/plugins/ directory. Go to the Plugins menu and activate the CKEditor for WordPress plugin.
You can check the demo site of CKEditor + WordPress to see the plugin at work as well as find some configuration instructions and tips.