I was never seved court papers or asked to appear. How do they get a judgement against you. And is that legal?

If someone got a judgement against you I would suggest you go to the courthouse where this was issued, ask the Clerk of Courts to look at the actual file and see just what happened on paper and just how they got this judgment. The court file is considered public information and you are entitled to look at it. You can have the clerk make copies of any pages you wish but you cannot remove or add any papers from this file. Take the copy of the judgment with you to the courthouse.

If you see anything in that file that is incorrect have the clerk make a copy of it and take it to an attorney to fight this judgment.

That first answer is correct, I'd like to add this though.
What you really want to know, and what is most important, is how did they serve your notice to appear for the court case.
While the most common way is to be served in person, obviously by your statement, this didn't happen. They could also have you served by certified mail, but you would know about that as well. The only other option, is to publish your original notice in a newspaper in your area and if this is what they did, they have to be able to prove it.
If they have no proof of service, you can motion for the judgment to be dismissed. I'll bet the did the published notice.
Good luck.

File Motion in the court to vacate the Judgment for lack of proper service, make sure you send a copy to the plaintiff listed on the judgment, certified mail.

This will set a hearing for the Motion to Vacate, if there is no record of service in the file the judge will vacte the judgment.

The plaintiff will have to start over.