Cardio helps burn calories to melt away fat, but if you want to build up your muscles and get chiseled lines, you need to strength train. When you lift weights, use resistance bands, do crunches, squats, or push-ups, it causes slight tears in your muscle fibers. This is necessary in order to tone up. When your body heals the fibers, your muscles strengthen and become bigger and more defined. In order for that to happen though, your body needs the amino acids in proteins to rebuild your damaged muscle tissue. So within 15 minutes to two hours after a workout, have a protein-rich snack. Some good options are yogurt, cottage cheese, a protein bar, protein drink, or nuts. Not only will eating protein benefit your muscles, but this nutrient will also help increase the absorption of water from your intestines and improve muscle hydration.
If you're wondering how much total protein you should have in a day, check out this chart.