To grant a user Content Editor access:

1. Go to Core > Security > Content Editor Access.
2. Select which Content Type to which you would like to grant the user access.
3. Mark the Display By User radio button. 
4. Click the Add Content Editors button or Edit next to an existing user. 
5. If you select Add Content Editors, find the user you are looking to add access for and click Add User(s). If you are editing an existing user proceed to step 6. 
6. Mark the checkboxes for the desired groups you would like to grant the user access to.
7. Click Save & Exit