In many states a summoms is legally served if it is left on your door,
And as mr yet mentioned you can ask for it to be dismissed if the service was not proper, if that court does not have jurisdiction and so on, but most service is legal and most courts that issue them have legal jurisdiction, and it does not make the court really extra happy for people to try and get a summons dismissed for false claims, so if you have legal claims to do so, then fine, if not, either go to the court house and get them to arrange a new court date if possible, or change your plans and be in court.
If they get that judgement, they can attach all of your bank accounts, they can garnish your wages and more.
Of course if you have the money in the bank, go down to the attorneys office and just pay them. If not arrange to be in court.