You might just get lucky. Just once, I was. When my middle daughter was born, I was 10 pounds lighter than when I had gotten pregnant with her. But you can't count on that, and I can tell you that from my own experience. Most women start out as new moms with 8 to 15 pounds more than they did before they had a baby.
That happens for a very good reason. God made our bodies to take care of us. Some of the weight you gained during pregnancy was meant to help you take care of your baby AFTER it was born. During pregnancy, your body needs an extra 300 calories a day to meet your baby's nutritional needs. A breastfeeding mother, on the other hand, needs at least 500 extra calories a day to make enough milk and stay healthy. Your body stores a little extra food in case there isn't enough food to meet its needs after the birth, when it's time to feed the new baby.
If you're breastfeeding, this is good news. You'll burn an extra 500 calories every day, which will make it much easier for you to lose weight. You might not even have to do anything special to lose weight. Just try to eat a normal, healthy, well-balanced diet. If you aren't breastfeeding, it won't be as easy for you. Your main goal should still be to eat well and exercise moderately to burn extra calories.
Another piece of good news for new moms. It's easier to work out. That's not quite right, though. It's easier to burn more calories. 200 calories are burned when you walk alone for an hour. When you walk with a stroller, that number goes up a lot. If you push a stroller uphill, it goes up even more. Things like lifting the stroller and car seat in and out of the car, carrying the baby up and down stairs, and just carrying the baby will give you extra work.
Still. If you have a few extra pounds that just won't go away, the best thing to do is exercise and cut back on calories a little bit. Just like you shouldn't try to lose weight during pregnancy, you shouldn't put your body through more stress by eating very little right after giving birth. Aim to lose about a pound a week, though it's likely that it will happen faster. Being a mother takes a lot of energy!