How to back up
The easiest way of backing up your files and settings is to let a backup application manage the backup process for you. A number of different backup applications are available, for example Déjà Dup.
The help for your chosen backup application will walk you through setting your preferences for the backup, as well as how to restore your data.
An alternative option is toto a safe location, such as an external hard drive, an online storage service, or a USB drive. Your and settings are usually in your Home folder, so you can copy them from there.
The amount of data you can back up is limited by the size of the storage device. If you have the room on your backup device, it is best to back up the entire Home folder with the following exceptions:
Files that are already backed up somewhere else, such as to a USB drive, or other removable media.
Files that you can recreate easily. For example, if you are a programmer, you do not have to back up the files that get produced when you compile your programs. Instead, just make sure that you back up the original source files.
Any files in the Trash folder. Your Trash folder can be found in ~/.local/share/Trash.