DriveHQ Online Backup is designed to automatically backup your files; once setup, you don't need to use it for a long time unless you see any errors. Online Backup can run as a Windows Service, so it can run even if nobody is logged on Windows. Also it can keep multiple file versions; so you might be able to restore an older version if you accidentally changed your files.
DriveHQ FileManager is designed to work like Windows Explorer (My Computer), you will likely to use it very frequently. You can drag and drop files, automatically synchronize folders. Folder synchronization works similar to backup, however it is not as safe as Online Backup. When you delete a file, the file on DriveHQ.com could also be deleted automatically. Also it cannot keep multiple versions and cannot run as Windows service. You can certainly use FileManager to backup files manually; but for automatic folder synchronization, it has a limit of less than 3000 files/folders for each synchronization task.