Alinah This is not really a Tonfotos question, as Tonfotos is not responsible for storing your photos or making backup copies. It only helps you to work and organise photos that you already store somewhere.
General rule is, you need to make regular backups of your photo archive. There are different ways how to do that, and that depends on how exactly you chose to shore photos, what OS you use and so on. If you are on macOS, there is very beatifull TimeBackup feature that can do all the back up tasks for you automatically.