If you're still at the scene, and if you're able to do it, assuming that you haven't been rendered unconscious or debilitated, is, you should take pictures. People have cell phones these days. Everybody has cameras available, so it's important to take pictures before the cars are moved from the scene. As many pictures as you can take, the better. That's the first thing. Now, of course, the police should be called, 911 should be called, if that's appropriate. I'm assuming that's all been done, but just from a claim point of view, documenting the conditions, the locations, the area, and the vicinity, is all very important, and you should do that. After that, and after your medical treatment, you should seek an attorney's advice on how to proceed.