Kettlebells are great for abs.
Almost every single movement you perform adequately engages the abdominal region.
By combining direct ab movements such as windmills and around the worlds with indirect ab work such as front squats and snatches, you can develop stronger and bigger abdominals.
Getting your actual six pack will be based on how well your nutrition is.
Combine high intensity kettlebell workouts with interval cario and a sound diet plan, and you'll be that much closer to a visible six pack.
Lets go over a basic kettlebell workout you can use to target the abdominal region: 3 rounds of:

• Kettlebell Figure 8's, 10 repetitions each side
• Kettlebell Russian Twist, 10 repetitions each side
• Rest 60 seconds

Perform this simple superset at the end of your regular Kettlebell workout.
Start off with just 1 round, and build up to 3 rounds as you get stronger.
Lets go over the movements: Figure 8

• Stand with your feet slightly wider than shoulder width apart.
  Place one kettlebell directly beneath and in between your legs.
  Keep your abs tight and back straight as you grab the Kettlebell with one hand.
  
• Now push the Kettlebell backwards, through your legs and grab it with the other hand.
  Swing it around to the outside of your other leg, and swing back past through your legs and grab it with the original hand.
  
• Think of dribbling a basketball.
  

Russian Twist

• Sit on the floor with your hands on either side of the Kettlebell, bottoms up.
  Bottoms up means that the handle of the Kettlebell is pointed towards the ground.
  You're holding the Kettlebell upside down with two hands.
  
• Keep your elbows close to your body and lean back until you feel like your falling backwards.
  Twist to the left side, keeping the Kettlebell steady.
  Extend as far as you can.
  Return to the middle and twist to the right side.
  

Make sure you master these two brutal movements before programming them into your workouts.