If you want to use CKEditor on your ASP.NET page, check the official CKEditor.NET Control. You can download it from the CKEditor download site and the full documentation along with installation instructions is available at http://docs.cksource.com/CKEditor.NET.
After you download the installation package, do not forget to check the samples that are located in the _Samples
folder and can be run as a standalone application without much work on your side.