Why does the phone says touch wiz stopped and the screen turns black

This happens when the device has basically run out of RAM as in too many apps running in the background, particularly common in an entry level phone like the J3. Touch wizard is the user interface and usually this fixes itself, if it doesn't you can remove the battery and then replace it which will restart the UI and close all those backgrounds apps. On newer version's with non-removable batteries you must do a soft reset to accomplish the same, by pressing volume down and power buttons simultaneously for about 10 second's until it reboots.