As you probably know, Sitecore bought Commerce Server somewhile ago and now we are starting to see the results of this integration.
Sitecore have released CommerceServer 11 and Sitecore commerce at the same time with the goal of keeping the two products together and transform in one product in the near future.
At the moment, you can feel that are two different products:
Commerce Server with the traditional business user applications and the same legacy backend (same databases and management console)
On the other SitecoreCommerceConnect that try to integrate CommerceServer with a set of DataProvider and out of the box integration bits
At the moment has been released as well a MVC application as a sample front end to consume Commerce Server and demonstrate how to use the API and the integration bits.
At the moment the installation process is not super-easy, but Ihope it will improve with the Sitecore 8 release and the relevant Sitecore Commerce Update