The black bar at the top of the screen, gives the options available to you in the National Product Catalogue. Below is a short description of what you can do in each option:
Itemlist: This is the module where you can see a list of all the items that have been published to you.
Price: This is the module where you can see a list of all the prices that have been published to you.
Subscription List: Here you will subscribe to suppliers so that their information can flow through to you.
Published Supplier List: A list of the suppliers that have published data to you. You can also Subscribe to a supplier's data from this module.
The Itemlist is laid out below. More information on using this screen is covered here.