What is a good excercise for your belly and the side bits ? like where i wear jeans a bit hangs out ?

im a size 10 but never realy had time to do tummy stuff.and when i wear jeans a hangs out a bit at the sides but my jeans are the right size if i was to get bigger they would fall down ..i just want to look good and b confidant in sexy clothes.whan i walk i feel my tummy wobble i hate it .but i have a bad back so i got to b carefull what i do and easy stuff..do crunches work?.help