How do you know for sure its a kidney stone and what can you do about it?
Depends in large part on the size. If it was a small one you may already have passed it. Larger stones can be more of a problem and can lead to other problems such as blood in the urine or a lot of foaming of the urine, which is from the excess protein going in the urine. Sudden pain in the kidney region can be a good indicator and the pain cannot be alleviated by changing the position you are sitting or lying in.
If you are still passing anything you can catch the urine in a glass jar and let it sit for about an hour to see if any crystals settle out to the bottom.