Read The Joy of Living: Unlocking the Secret and Science of Happiness by Yongey Mingyur Rinpoche. It will answer all your questions about meditation, how and why it works, what method is the best for you, etc. You can buy it here.
If your back hurts while meditation or you have headaches often or something else, you can use your pain as an object of meditation.
When you try to ignore something you feel, it comes up all the time, but if you are not afraid to sense it, in some time it disappears. Just slightly turn your attention to the pain and try to concentrate on it for some time without thinking that pain is bad, it's just pain that you feel.
Use this method only if you are sure that your pain is not dangerous, in some time you will stand any kind of pain easier.
If you don't have time for a formal meditation, use this method on the go.
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