They can sue you in hopes you do not defend the case. (You do not file an Answer)
In which case they get a default judgment and take action such as garnish your wages.
As to what you can do, like you said
file an answer is a start. However, filing the answer is only the beginning of fighting the case.
Here are your choices:
1.) Fight the case, pro se.
2.) Give in and pay them and/or let them win a default judgment.
3.) Get an attorney to fight your case.
For more detail on 1, see this post:
http://www.expertlaw.com/forums/showthread.php?t=41715