How do you file a claim for an accident that was caused by someone else?

If you know their insurance company contact them, and report the claim, with all information you have. If you do not have their company (and they will not give it to you), contact the dmv for your state and see if they carry those records (assuming you have the license plate). If you know the company and just not how to contact them etc, most (if not all) companys have web pages that will give you info, google ''filing claim with state farm'' for example.