Does doing sit ups help burn belly fat? Or is there any other exercises that will burn belly fat and help tone up a bit?

Stop belly fat? Unfortunately regional wt loss is impossible by any excercize or targeted diet. A good general weight loss program combined with an aerobic fitness program 30-60 min/day 3-5 days/week within your body's capability is the way to go. Good luck and go for it.
Tone abdomen. Sit ups tone ab muscles and burn a slight amount of calories. Reducing overall caloric intake will have a bigger effect on definition.