is it possible to flash supersu on my phone with twrp without unlocking bootloader I was wondering if you could get supersu somehow on my device, also what is the difference between not flashing supersu and downloading it, becuase I think I saw a article about being able to flash supersu without unlocking the bootloader.

Also if you say just to unlock the bootloader and flash supersu, but I like my phone with everything and I don't want to wipe it.

Also I am on marshmallow 6.0.1
There's no chance that you flash TWRP before you unlock your bootloader, not even SuperSU.

A recovery can only be flashed from an unlocked bootloader, or a rooted system. But as you have neither, you can't flash TWRP, which is required for flashing SuperSU.