Learn how to do a back roll with master Judo instructor Richard Acuna.
Here is another video on how to do a back roll where you can see other variations depending on how good you get at this. There is the basic back roll from standing and squat position, then might be able to add a handstand too. GMB video tutorial explains each step and tells you what you need to pay attention to. Find what works better for you, stick to it and make progress from there.
Please take into consideration to work on these exercises with supervision from someone with experience. Find a local gym trainer who specializes in these acrobatic moves to assist you with every step to master your needs.
Your back and neck can get seriously injured if you are not careful enough and again find someone who can assist you, help you and guide you.