To add a product click the "Add Product" button on the Shop Manager page.

Then enter in the information for the different sections on the Add/Edit Product page.

First add a item title and description.

Then in the Product Data section you add your item details in the different tabs:
In the General tab add a item price.
In the Inventory tab you can manage stock quanity if required.
Use the Shipping tab to enter a shipping price for the product.
Use the Product Options tab if you want to to add different options such as size or colour.
( Click here for more details on how the Product Options work )

Add a category for your item in the Category section.

You add your main image for the item in the Product Image section.
If you have any extra images you add them in the Product Gallery section.

After you have entered in all of your details click the Update/Publish button to save the changes.