To create new items, you should be either an Owner, Admin or Sales Manager for the account.
From the Menu, select the Item Catalog where you wish to add the new item. If you do not have any Item Catalog created, see this link first.
Once in the Item Catalog, you should see "Add Item"
Below are the fields to complete when creating a new item.
After completing all the necessary fields, submit your item. If there is a quantity associated with the item at the time of creation, customers will now be able to order this item from your Item Catalog.