Steps to get fit.
1: start weight training. No this won't make you big! It will However add shape to your body when your body fat% drops. 3 45-60 min full body workouts a week should be plenty.
2: start doing cardio: this is just a little something ekstra we do to burn a bit more fat. Find a type of cardio that you like to do and do that. It can be running, swimming, biking, weighted, tabata, hiit. Try it all you and let us know what you like best :)
3: start a diet. Not just eny diet. One you can Stick with forever. Succes is not a sometime thing, but an all the time thing. So don't do something you can do all the time.
Parsonally I really like a paleo stile diet. With lots of Meat, fruits and veggies. The good thing is that you can eat as much of it as you want, it's easy to Stick to, It taste good, you got tons of options. And the best part is that you don't really have to worry about slipping off once in a while.
Follow these tips and u Will be gorgeous in no time
Hope my advice is appriciated :)
Edit: if you just want a flat stomach there is no point in doing ab work. Ab work Will only help your abs grow and become more visible. Not make them flat. So only do ab work if you actually want defined abs.