Simply login to your 1shoppingcart account, and click on the "add product" icon.
There are only two pieces of information that are absolutely required, everything else is optional. You need to get the product/service a name and a price. That's it! If you go ahead and do that, hit the "save" button at the bottom.
You can now view your order page I simply clicking on the "links" tab and click on the "test" option which will open up your new order page in your browser. Of course there are many other options to set if you would like to, such as choosing an autoresponder to subscribe when someone purchases a product, discount prices, tax and shipping info, etc.