Process:
a.    Writ issued—asks appropriate questions.  Someone who supposedly has property of the debtor, or owes a debt to the debtor is issued a writ asking to verify if that is the case.  A bank account may be considered a debt owed to the debtor.
b.    Command not to pay.  The party is given a command not to pay any debt or turn over any property to the debtor. A command not to pay the debtor may stay in effect until released by the court.  If a party turns over property of the debtor, on in the case of a bank pays a check despite this order, they will have to turn over an amount equal to what they had before they violated the order.
c.    Answer filed.  The party must file an answer stating what they have.  They may state that they hold nothing, or that they have a superior right to the property held.  A bank will usually assert a defense to a garnishment writ, and will usually say that the debtor owes them a loan.  Typically they will win.  If any additional property is received after delivery of the writ and before the answer it should be turned over to the creditor, or included in the amount stated in the answer.