An APA file is a backup or archive of the MED file and sub-folders for the application. To create an APA file, you use the "Application Manager" to "backup application". The Application Manager is a separate software to View Studio. You can open it through the "Start" menu in Windows:
Start>All Programs>Rockwell Software>FactoryTalk View>Tools>Application Manager
Or...
From within View Studio:
Tools>Application Manager...