The best ones are squats and a plank. If you don't know how to do them search on Google or ask your local gymnastics/gym.
I don’t really plans on giving a long or so much remarkable answer as I am too tired or let me say exhausted in other words ,the best answer is back hand chaired exercise it’s good for the back bones
Find a wall, lay flat in front of it, climb yourself up and hold this position. Your legs should be straight back and your back bent while your hands hold you up. For a deeper stretch, get closer to the wall.