Have you purchased a dsIDXpress license from us yet? It sounds like you may have downloaded the plugin and have activated it using the Sample Data.
In order for the plugin to populate your own listings you do have to purchase a license, go through an approval process with your MLS, and then at that point you'll be able to display your own listings, create pages with listings for various communities / subdivisions / zip codes / etc.
You're also able to display listings using one of many widgets that comes with dsIDXpress.
Please let us know if you have any additional questions or concerns.