Having a baby changes your body. Some things may never be quite the same again, but other changes don't need to be permanant.
You can tighten your tummy with excercise, for example, and any weight you've gained will gradually drop off if you eat healthily and exercise.
It won't happen overnight. It took nine months to make a baby, and it could take at least that long to get back into shape again.
You can find out more about the changes to your body immediately following birth on the NHS UK website.