To add an item using the Add Like button is the easiest.
In Management Console, go to Merchandise>Modify Merchandise.
Click on the Screen Group on the left where you would like to add the new item.
Highlight the existing items on the right with the same characteristics as your new item (Links, Category, print route, etc.)
Change the Name and the Base Price of the item.
Click the "OK" button to save the new item.