At the moment, you're only able to create and edit email response templates when you click Reply next to an active customer comment (it's an annoying quirk - we know - this will be fixed up when we release our new Messaging Portal...watch this space!)
In the meantime, here's what to do:
Step 1: Click on the Ratings tab along the top toolbar
Step 2: Click the Reply button next to any active comment (don't worry, you won't need to send a reply unless you want to!)
Step 3: Click the Create New Response button on the left-hand side
Step 4: Add a subject line (this will be visible to your customers) and write your message
Step 5: Click the Create new template button down the bottom to ensure your new template is saved
Step 6: At this point, you can either send the message or click cancel
Step 7: That's it!