A lot of people make the mistake of just doing thousands of crunches and hoping for abs. The truth is that you need a good combination of cardio, strength (e.g.cCrunches), and a healthy diet to get abs.
People tend to struggle a lot with stomach flab and crunches do not resolve the issue. Focus on eating well, lots of cardio to burn the fat, and then strength training to build muscle tone. I am not a fan of regular crunches as they strain the neck if not done right, so I get my strength from other forms of abs exercises like v-sits, planks, and even deadlifts.
Cheers Eights & Weights!