Based upon your answers, your back pain is most likely due to muscle strain, sprain or other minor injury, perhaps related to recent activities that triggered it. The pain should go away over time.
To decrease pain, avoid overuse, rest briefly if necessary (but avoid complete bedrest for more than a day or two as this appears to provide little benefit in most cases), and avoid those activities that might have triggered your pain in the first place. Over-the-counter pain medications, topical medications (such as Icy Hot or Ben Gay), or the application of ice may be helpful.
If symptoms are getting worse or do not go away, consult your physician.
With mild pain that has only recently started, exercises can be helpful to stretch and strengthen the back. If there is severe pain, avoid these, but otherwise, do those you can easily tolerate as they may hasten your recovery.