To activate CKEditor for SharePoint for a site collection, go to the Site Actions menu in the root site of a site collection, and choose the Site Settings option.
The Site Settings page is used for the configuration and administration of your SharePoint site collections and sites.
From the Site Collection Administration section choose the Site collection features option.
Find the CKEditor for SharePoint feature on the site collection feature list. If it is not active, click the Activate button.
Once activated, CKEditor for SharePoint can now be used on your site collection.