people don't say turn to left. they say "turn to the left" or "turn left"
turn left means go left. examples: "when you reach the first stoplight, turn left" "walk that way for about 5 minutes and then turn to the left when you see a mcdonalds"
turn on means put something in use. it's the opposite of turn off. examples: "turn on the lights" "turn off the lights" "turn on the TV" "turn off the TV"