If you placed an order and there was a problem with the order, be sure that you try to contact the store owner first. Allow them some time to reply back to you, and understand that it might take a few days before you hear back.
If you have tried to contact the store owner and have been unsuccessful, you do have the option of filing a dispute, especially if you didn’t receive what you ordered. If you paid via PayPal the instructions for filing a PayPal dispute are available here. If you paid via credit card you can just give your credit card company a call and let them know that you need to file a dispute (chargeback). Please be certain that you use this as a last resort - filing a dispute against a store costs them money and damages their reputation. If the dispute is found in your favor then the money will be returned to you by your bank.