Back up data to SSD

About to back up data to external hard drive – SSD. Old MBP. Ubuntu Budgie 20.04 (I think). Will use cable.
Want to manually start back up like once a week or similar.
Only the files which have been changed from last back up should be saved.
I’m almost rookie about Linux Ubuntu and need detailed help to make this come true.
Grateful for all help.

We ship deja dup backup and restore software in later versions of UB.

For 20.04 you can install this via the software center

… and here is a handy guide to describe how to use