Hi My*Evergreen*Closet,
The custom items specifics tool basically allows you to create your very own item specifics. When you click the "Custom Item Specifics" link on the listing creation page, a pop up window will come up that has two fields labeled "Detail Name" and "Value" that can be used to enter your item specifics.
If you would like to indicate that a garment you are selling is size medium in the custom item specifics section, you would enter "Size" in the "Detail Name" field, enter "Medium" in the "Size" field, and then click the "Add" button. You can then repeat that process for any additional custom item specifics you'd like to add.
I hope this helps. If you need any further assistance with this, please feel free to contact our customer support team using the form on the following page of our site:
http://www.auctiva.com/help/requesthelp.aspx-Mike