This applies to both Listing Templates and Listing (aka item)
Simply select the item by clicking on it in the Grid
The details of the item will be displayed in the Simple Editor
Edit the details as you need
To Save the changes you made, you can do any one of the following:
Select a different item in the Grid
Click on the "Save" button
Click on the button "Save & Verify" to both save the changes as well as verify with eBay the details you entered. In case any errors are reported from eBay, they will be displayed in the "Submission Errors" area at the bottom of the Simple Editor.
Click on the "Submit to eBay" button to both save the changes made as well as send that item to eBay. If no errors reported by eBay, a new listing will be created on eBay.