To answer to your question of How to start working out again, it is important to check with a fitness coach first before you start working out again. That way, you will be guided on the kinds of exercises to do first in order to prepare your body for a more rigorous workout regimen. This will not only help you avoid injuries, but will also make sure that you achieve your goals properly.
Professional advice is necessary when doing anything related to your health and body. Though it is safe for you to do some light workouts like stretching and cardio, make sure that you are under the watchful eye of a trainer when lifting weights and doing other forms of heavy workouts.