So you have managed to add the Clonezilla ISO to your Grub boot menu and can boot it.
When you do, you are now in the live system which Clonezilla provides
and you are asking about how Clonezilla works, how to use it to create an image of your entire disk?
I assumed you are talking of the first point in this HowTo:
how to make a cold system backup
[HowTo] make a crash-proof backup in Manjaro for your entire system