If you have custom catalog data in the older ARI E-Commerce platforms you can have it exported and imported by following this guide.
If you are starting from scratch you will have two different options for cataloging your private/custom products and getting them into the E-Commerce Configuration so that you can then list them to your webstore.
Option #1 - User Interface
This is a great option for creating one product at a time and dealing with less than 100 products. For detailed instructions, Click Here
Option #2 - Import csv File
Create products by importing a structured csv file into the File Center. This is the way to go if you are looking to create products in bulk. Recommended for anything more than 50 products. For detailed instructions, Click Here