Turns out, I was looking in the wrong place. But customer service helped me find the Cart page and then your instructions were perfect! Thank you! 

It's still not working. Do you know if there are features like that that I just can't access until I'm using a paid version?

Thank you for your reply! That looks like it will probably work, but there isn't a "cart" option for me. I'm just checking out one of the 2.0 themes with the free trial version of Shopify. Do you think that is the problem? I'm totally new to all of t...

I'm offering postcards with custom, handwritten messages. How do I set up an option for my customers to be able to input their message at the time of sale? Thank you!