How much trouble are you in if you cause a rear-end car accident?
OK, you just rear-ended somebody and you're wondering how much trouble am I in.
Well, the good news is, if you have insurance probably not much. Your insurance will take care of it. They'll hire a lawyer if necessary. Normally their insurance adjusters will take care of the claim.
If you have been in a wreck like this, call your insurance company, report it, ask them what to do. They'll tell you.