This depends on the status of your order:
If your order was cancelled:
The charge on your card was only an authorization (pending charge)
This authorization will disappear after your bank processes it
You will not see a separate refund, the authorization charge will simply drop off
If your order was delivered and then refunded:
Refunds are processed by the store
Most refunds appear within a few business days
Timing depends on your bank or card provider
You can find the store's contact information on the receipt that was emailed to you, or by clicking on "More info" on the store's delivery website under the store description.