How do I create a .iso file of my personal Linux Lite system

[justme2]

But isn't an external or 2nd drive a necessity for any backup system? Backup to main drive =  loss of backup if drive catastrophically fails.

An external drive is definitely not a requirement to backup. A second drive is probably recommended, but in the case of this laptop I have only one physical drive. 

I did say external OR second drive but not a good choice of words on my part.
Users who have one laptop with one HDD and no space for a second drive need to consider an external drive to secure their backups. In my experience most users only have one machine but I don't know how that compares with members of this forum, who probrbly have a greater interest in the technicalities. A survey may be of interest! No matter what method is adopted, security of a backup is priority if averse to risk.