Hi
Server adapters in Eclipse allow you you interact with the server they're bound to.
In case of OpenShift, the server adapter allows you to publish the changes in your project (the project that you imported to your local workspace in the OpenShift application wizard) to the OpenShift Paas (application).
Since OpenShift deals with git repositories, the server adapter's more or less a shortcut for pushing your local git clone to it's origin.
Cheers
André