New to this

If you're going to a gym there are two things I do. I don't know the names of the equipment but the first one you stand up on and then dangle your legs with all your weight supported by your forearms. You then bring your knees up to your chest repetitively. Don't let your legs go completely slack on bringing them down each time. It is basically crunches but it ensures that you are doing it in a way that won't damage your back.
The second piece of equipment causes you to lay on your back with your knees bent and held in place by a cushion. Your head will be lower than your knees. Before getting on grab a medicine ball. As your core gets stronger you can up the angle for higher difficulty. Once you are on, grab the medicine ball. Pull yourself up with the ball and extend your arms (holding the ball) to the left, center, and right pulling the ball into you between each direction. Lower yourself back (not all the way) and back up to start to cycle again.