HELP!! How do I back up all of my pics to an internal SD Card I added?

I already changed the option in the camera settings but how do I move all of my existing photos from others and screenshots to the SD Card.

You'd need to move all files manually using a computer or using a File Manager to move the files to the SD Card (if your phone is running KitKat, then only the stock File Manager will work as 3rd party file managers are restricted in this version of Android).