There are two parts to installing CKEditor for Drupal 7 (Drupal 8 comes with it already installed):
- The CKEditor Drupal module, which is placed in the
- The CKEditor library, which is placed INSIDE the
After installing the module and library, enable the module and it should take effect immediately.
If you want to customize your CKEditor settings, look in the administrative configuration area under Content Authoring -> CKEditor.