In the /home/yourusername directory, there is a hidden folder called .minecraft. If in LXDE (startx), to be able to view the .minecraft folder, you have to right click in the File Manager and check Show hidden files, assuming it isn't checked already. Next, open the .minecraft folder, and keep opening the folders in it until you reach the folder that your worlds are in (minecraftWorlds). Then copy all the world(s) you want to backup to where you're backing up to. You're done!
To restore from your backup, just go through the same process of opening the folders in the .minecraft folder in /home/yourusername. When you reach the folder where your worlds are kept, copy the world(s) from your backup to there.
Please note this will delete all changes made to the world(s) since the backup, although you can choose to have the world(s) from the backup and the current world(s) both, if you rename the current world(s)'s folder before copying the world(s) from the backup to minecraftWorlds.
I hope this helped!
hello world