If you don't pay a debt, a debt collector generally can sue you to collect the money due.  If they win, the court then enters a judgment against you.  The judgment states the amount due and allows the collector to get a garnishment order against you, directing a third party, like your bank, to turn over funds from your account to pay the debt. 

Wage garnishment happens when you employer withholds part of your paycheck to pay your debts.  Your wages usually can be garnished only as the result of a court order.

Do not ignore a lawsuit summons!!!  If you do, you lose the chance to fight a wage garnishment.