Yadis! Backup is a free and simple backup application, that will copy your files to almost any destination you want, preserving or not the structure of your directories.
Marked folders are backed-up in real-time (no scheduling needed).
Whenever you make a change, Yadis! makes a backup, and if your backup destination isn’t available, it remembers the changes and whenever the location becomes available Yadis! will backup your changed files.
Yadis! Backup comes with a full manual that will let you know how to use the program.