system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference(s) between using debit and credit cards when purchasing something?

my bank card allows for both options (as I understand is common) but I never really fully grasped the difference.
gpt
I think op is asking what's the difference between using his/her debit card as debut or credit when making a purchase. 

When you use debit, you have to input your pin, and the money is automatically deducted as if you made a withdrawal at an ATM. When you use credit, the transaction is processed by visa/MasterCard and a preliminary hold is placed on your card for the purchase price (sometimes a little more or less depending on if you're buying gas at the pump or dining out) to verify that your card has enough available credit to handle the transaction, but the money hasn't technically left your account yet. After the hold is released (anytime between a few hours to a few days) the hold is released and the funds are drawn from your account. You can't debit more than you have in the account, whereas credit transactions will sometimes let you overdraft your account (usually costing you a bank fee). Some banks offer rewards programs for using your card as credit which you can redeem for cash back, gift cards, merchandise etc.  Also, it'd worth noting that the places you're spending money are charged different rates for running your card depending on if you use debit or credit. Most credit cards charge the business 1.5-5% of the transaction amount, whereas debit fees are capped (in the US) at $0.24 per transaction plus 0.05% of the swipe.

EDIT: changed some of the figures for rates per TYMSMNY below and some internet research :)