In Minnesota, a debt collection lawsuit begins when the defendant is served. "Served" is just a fancy legal word that basically means "delivered". There are two main ways you can be served by a debt collector: (1) by having the lawsuit handed to you personally; or (2) by having it left at your home with someone of appropriate age. Once you've been served, you have 20 days to answer the lawsuit. An answer is a formal legal document that responds to the allegations in the complaint. If you don't respond within 20 days of being served by a debt collector, they can apply for a default judgment. The court considers all of the allegations in the complaint to be true and gives your opponent whatever they are asking for. In other words, your opponent wins not because they have a better case, but because you didn't participate. In debt collection cases, a default judgment is entered administratively by a court clerk without a judge ever seeing the case. Debt buyers love to get default judgments against consumer because they don't have to present any evidence to a judge.
A judgment, whether entered by default or otherwise, is a court ruling that you owe the money. And once a debt collector has a judgment, they have the power to garnish your bank account and your paycheck. Although judgments can sometimes be overturned, for the most part they are final. That's why its so important to answer the lawsuit within the 20 days. If you don't, you no longer can raise any defenses and will probably have to either negotiate a settlement or payment plan with the debt collector or, if the situation is serious enough, consider bankruptcy.