You may want to lock your email templates to prevent other users (besides admins) from making changes to your content. While users can still see the template from Tools > Email Templates, they will not be able to edit. However, all users can select the template for an email send, but any changes made to the template on the send will not save over the original template.
If you have already created the email:
Find the email template in your list view and click into the name to see the template detail view. In the Email Info block on the right hand side, select the pencil to make edits.
Change the Locked drop down to Yes or No.
If you are creating a brand new email:
You will see your locking options on the Confirm & Save page. You are able to move the slider to Locked or Unlocked. When locked, only admins and the creator of the template can make edits.