How to push forms to aggregate

I feel this may be a simple problem, but I can't figure out how to push blank forms from ODK-Briefcase to ODK- Aggregate. The documentation says
"""Select the forms you want to upload and click Push. The selected forms will be pushed from ODK Briefcase Storage on your local system to the Aggregate server."""
However the list of available forms is (understandably) blank, as I didn't do anything to 'add' a blank form to Briefcase. I tried placing a copy of the xml form in "ODK Briefcase Storage/forms", but it just gets deleted when Briefcase starts up.