Key would be listening to your body. If there were no complications to your delivery, and you were active right up till the end of your pregnancy, you can resume some light exercises and stretching as long as you feel up to it. If you were not used to exercising regularly before or during your pregnancy, start gradually. You could start with pelvic floor exercises to help strengthen the pelvic muscles. Also, taking your baby out for walks is a good way to start as well. When you feel your strength returning, you can start taking longer walks or picking up the pace. Most importantly, listen to your body. Adjust the duration and/or intensity as required. Give your body ample time to recover. Some exercises to avoid are sit-ups, crunches, higher impact cardio (like running), and swimming (at least until your postnatal check, and have went through seven days without postnatal bleeding or discharge. This is to avoid infection. Best to check with your doctor before going for a swim). Here a useful article on how to ease back into an exercise routine after delivery: http://www.fitpregnancy.com/exercise/postnatal-workouts/8-steps-easing-back-fitness-routine-after-birth
I resumed my exercise 2 mths after delivery. Gynae told me as long as u feel comfortable, wounds have healed, then I m good to start my normal exercises. I guess it is also dep on indiv's comfort level too. My friend who is a gym fanatic, started her gym workout a month after her confinement.
Most of friends start a month or two after delivery. They would start by trying to walk at least 8000 steps a day (you can download an app to help you keep track). Yoga and light stretching helps too. After about 3 months, they could resume normal gym routines.
I am a mummy of caesarian, I start sit up & trek running after two months. For natural delivery, definitely can do all these after confinement. Healing will be faster for natural delivery mummies.