After Selecting it fill there required details, there will be 3 fields after selecting Google Drive namely Location Name, Protocol(which we have already selected as Google Drive), Backup Location(which is a optional field).Location Name: It just work as an identifier to identify a particular location as multiple locations could be set on Google Drive.
Backup Location: Its the folder you want to upload your backups, if left blank it will place the backup at the root location, which is inside the Backuply folder that is created when you give Backuply access to Google Drive and all your backups go inside it and in there the Backup Location folders are created.