How are purchases done so fast?

[deddod]

I think, After confirmation to enter in blockchain although still 0 confirmation, I think you do not have to wait long until confirmation is complete, because when transaction enters in blockchain then the transaction can not be canceled. 

[Noctis Connor]

When you buy something with bitcoin and the transction are being made or unconfirmed its done it just need a confirmation with the blockchain before it will be transfer successfully and after the confirmation it will be confirmed to the store that your transaction is done and fully paid. Your Transaction is Completed.