Being sued

I recieved paper work last week from a law firm that states I have been sued. I called the court house and it is in fact true. The paper work states I have 20 days to respond. Also there is a certified copy of the letter still sitting at the post office. When does the 20 days start. Should I have recieved a summons as well? How do I answer this?

The debt is about $7k that is mine but they refuse to set up a payment schedule. I dont have the money to settle.

If a judgment is granted I know they can't garnish my wages but can they go after my bank account even if its a joint account?

Any help is appreciated.

Thanks