Why do we use xrays?

You are a bit confused. They don't. If you mean "why are X-rays held up to the light to see details," that's different. X-ray film turns dark when irradiated. Then the film is developed so that people can examine it. I don't agree. X-Rays are a form of light. A light, precisely. However, they do not "use" light waves, and the person above me is wrong in that sense, and does not know that X-Rays are a form of light. They don't use light waves, they are simply in that form - light waves - because that is how they work. I don't know quite how to explain it, but it is not a sound wave or any other type of wave, only light. They are very small, which is why X-Rays show your bones. However, they have radiation effects. (Notice that radiate means to radiate heat, which comes from light?) These effects can only happen with light waves.