Usually wage garnishment works like this: The creditor sues you, obtains a court judgment, and then solicits the help of a sheriff or other law enforcement officer to garnish your wages. The maximum the creditor can take is 25% of your net pay. If you can't live on only 75% of your wages, you can challenge that amount in court.
There are a couple of exceptions:
To help you evaluate your debt situation, see Solve Your Money Troubles: Debt, Credit & Bankruptcy, by Robin Leonard and Margaret Reiter (Nolo).