To start with you need to download the latest stable release of CKeditor.
Extract the downloaded file and place the ckeditor/ folder in your applications webroot directory. (beside "protected" and "css" and other directories)
For those who feel, the Controller->accessRules() or RBAC (Role-Based Access Control) is too complicated or doesn't want the username(s) to be hard-coded in accessRules(), here is a very simple, easy-to-implement solution.