You have already installed osCommerce on your account and now its time to get started. Check this tutorial for the basic configuration steps of the application:
1. Login to your osCommerce Admin Backend
2. Go to Configuration section on the top left corner. A new page with different chapters will open.
3. Select a chapter and click the Edit button on the top right
4. Make the needed changes
5. Hit Update
There are various sections in the Configuration menu, which are divided in different important topics you can cover. You can now go ahead and build a good foundation for your online shop.