Everyone has abdominal muscles, whether we can see them mainly comes down to good dieting.
We must also train the abdominals hard to bring out and accentuate the muscles.
There are so many different ab exercises to choose from, most of them will work so try out a few different ones, and see what works best for you.
Make sure you hit the upper, middle and lower abs and train them with equal intensity. Hanging leg raises is good for hitting lower abs, most movements that involve the legs being raised will hit the lower abs whereas chrunches and decline situps will bring in more upper abs.
Build up ab strength in the begining as you would with any other body part, by progressively adding resistance/weight, however be sure to keep the tension on abs at all times and use slow steady reps until your abs are so sore, that another rep is impossible.
Adding a twist at the top of crunching movements and leg raises will bring in the obliques, however be sure to work these with isolation exercises.
Try seated twists to firm and tighten your waist.