What happens in a two car rear end crash?

Not certain I'm understanding the question ''two car rear end crash'' assume you mean if one person rearends another...File the claim with both companys (yours and the person that rearended you), of course, the vast majority of the time, the rear end driver is responsible/At Fault. Assuming his company accepts liablity they will repair your vehicle, put you in a rental while yours is down, and pay you for medical bills and injury settlement once you have finished treatment (if an injury).