Very little. They are interchangeable although "worry" is the more common and the more versatile. I would say "fret" is a more formal or certainly an older word. I wouldn't really expect anyone below the age of about 30 to ever really use it. Perhaps "fret" has some more immediate or active connotations. Personally I wouldn't say that you could be "fretting" about something totally different whilst on a day out for example - you would need to be more in the moment of actual worry. "Worry" could take many forms including some long running passive concerns you may have and so you could be worrying about how you were going to pay for everything when you out shopping for example.

"Worry" is the common, everyday word. "Fret" is rare. To me, "worry" suggests anxiety that is focussed on one single, fairly important thing. "Fret" suggests one of many small, unimportant worries. "I am worried about the surgery I need to have." "I'm fretting about all the things I need to do tomorrow. I have to mail a letter, buy groceries, do my laundry, get my hair cut, and deposit a check at the bank."

Your broken sentences make no sense.

I found already When I fret over something, it engage my mind. F ex not fret about me while I am driving fast. else you say worry not worry about me