Installation instructions:

This module depends on the yui module so you need the yui module installed.

1- Download the module to your modules directory sites/all/modules/

2- Enable the module from admin/build/modules

3- Go to the module settings page on admin/settings/yui_editor and define 
where the editor should replace the normal textarea

4- Give access permission to the user roles you want to be able to use the editor.

5- Make sure you use the full html input format for the editor's output to work.

That's it, have fun :)