Other answers cover the differences between the types of card (debit vs credit vs charge). However, there's another layer of important differences - the card processing network and the processing method used for a specific transaction. In some cases, this can cause card types to behave differently on a transaction by transaction basis.
When you swipe a card, the merchant uses their own bank to collect money for your transaction. Their bank talks to a card processing network (Visa, Mastercard, etc) in order to submit the transaction to your bank, i.e. the bank that issued the card.
Most card networks handle many different types of cards. For instance, VISA handles debit cards, gift cards, and credit cards. Further, over time, the features of those cards have evolved and changed over time, and different issuing banks may issue different card products that have different features (as an example, in the past, data about the card was encoded on mag stripes, whereas now, cards generally also have a chip on them). Even within the context of a single card, a merchant may be able to submit the transaction different ways:
- via reading the magstripe,
- reading the chip,
- manually typing the card number into a console,
- using a stored token from a prior transaction,
- reading a contactless chip in the card,
- communicating with a payment app on a cellphone or smart watch which has been linked to the card.
Further, some networks allow a transaction against a debit card to be submitted via their debit card channel, or via their credit card channel.
Most of this is invisible to consumers because it happens automatically, but some merchants essentially put the consumer in direct control. For instance, in many grocery stores, the clerk checking you out will ring up your items, and there will be a POS console in the checkout line facing the customer. The customer will swipe or insert their card and actually carry out the transaction - the store clerk never actually sees or touches your card. Often, this arrangement puts the choice of transaction style in the consumer's hands - you can choose to swipe the magstripe or read the chip. If the network your card is on allows transactions on your card type to be submitted via different channels, you will sometimes be presented with that choice (for instance, you may be prompted to choose to submit the transaction as a debit or credit transaction, although the choices presented on the console rarely actually spell that out - instead they often say something cryptic like "US MASTERCARD" for submitting a credit transaction).
Ultimately, the end result is still the same from a consumer's perspective - the transaction hits your account and the merchant is paid. However, there are a few differences from the bank and merchants' perspectives:
- different transaction types will incur different interchange fees. A merchant may receive slightly less money for a "card not present" debit card transaction versus a chip-read credit transaction.
- different types will result in different responsibilities from a fraud perspective. If the transaction is submitted in a way that's considered more secure, the banks assume a larger portion of the risk, versus the merchant. This is often an incentive for merchants to prefer more secure transaction types.
- different types will result in different timings for the money actually leaving your account. Many banks run credit card transactions in real-time but batch debit card transactions.
I'm adding an edit to address additional points you made in your edit to the question:
For example, what I already learned from the few answers that have been posted here, in the US you cannot access your credit card account directly. You can see balance, you can pay it off, but you cannot treat it like another bank account.
In the US, cards of any type are essentially just instruments for accessing an account. Typically, card types and account types are strictly linked: a debit card can only be linked to a deposit account, and a credit card can only be linked to a credit card loan account. There are other subtle variations on this theme though - for instance, some institutions will issue a special kind of credit card linked to a line of credit instead of a traditional credit card loan. And even more confusingly, there are cases where other mechanisms traditionally linked only to deposit accounts can be linked to loans (for instance, a bank may allow checks to be written against a home equity line of credit).
It's also important to point out that cards (of any time) are not inherently linked 1 to 1 to accounts. In other words, if you have a deposit (checking) account, you can have no debit card at all. Or one debit card. Or 4 debit cards, with different card numbers and different people's names on them. The same holds true with credit cards - one person who opens a credit card can add other users to their loan, and have the bank issue each of them their own card. All the cards are tied to the same credit card loan, and transactions on all of them end up impacting that single loan.
I've also read between the lines that credit cards might be issued not only by banks but other businesses too.
It's common for various merchants to issue cards with their own branding (i.e. the retailer Target has their own credit card). Sometimes, these cards are "private" in the sense that they can only be used at that merchant. But other times, the branded card can be used anywhere (for instance, Amazon issues cards that can be used anywhere, but earn extra rewards if used to buy things from Amazon). Confusingly, these cards can be implemented in many different ways:
- sometimes these cards are actually operated by the merchant directly. No bank or network is involved.
- sometimes the cards are co-branded with a network, and use that network to submit transactions (i.e. Amazon's VISA card product).
- sometimes the cards are operated by a third party bank, even though it's the merchant who "issues" the cards to consumers (for instance, the hardware store Lowes has a private account that's operated by a third party bank).
I can treat the credit card account just like a regular account, I can keep extra money there, send and receive money via internet banking, etc.
It's important to clarify that, largely speaking, this is mostly true in the US as well. For instance, if you get a credit card from Bank of America (or just about any other bank), you can use their internet banking tools to manage the account. This can mean doing things like paying your credit card bill, or sometimes even things like using your credit card to submit payments or "transfer" money (essentially taking a cash advance from the card) to other accounts. In fact, if you use one bank for your credit card and your deposit accounts (say, a checking account into which you have your paycheck direct deposited) you can typically log in to one internet banking console and manage your various accounts from one place, even though they are technically separate accounts. So, in practice, you do usually have access to the account, it's just treated separately from your other accounts.
The one clear differentiating factor is that the loan behind a credit card is a distinct and separate account from your deposit accounts or other loans. This is important due to the way the US banking system manages reserves and other operational and financial concerns. Banks in the US are required to keep a certain amount of cash on hand, based on the types and balances of accounts they operate. This cash on hand generally falls into two categories:
- Reserves to protect against losses from loans. If a consumer defaults on a loan, the bank needs to have cash to offset that loss. Banks are required to reserve against these losses to make sure they can continue operation when they have losses.
- Reserves to protect against withdrawals from deposit accounts. Banks need to keep cash on hand so they can give it to consumers who withdraw it from deposit accounts, in order to stay liquid if or when consumers want to use their money.
These two types of reserves are calculated and managed very differently. Because of this dual approach to reserves, banks need to have a strict separation between account types. If a bank were to offer a single product that let consumers use an account in either state at will (either as a loan, if they charge a lot of credit transactions, or as a deposit account if they put a lot of money into the account such that it has a positive balance), that account type would be impossible to reserve for, in our current model.
So, banks maintain strict separation between account types. Actions that are normally associated with a deposit account (depositing a check, direct deposit of your salary, etc) aren't allowed on loan accounts, and carrying a positive balance on a credit card isn't typical. Also, actions that are typical on a credit card (running a "negative" balance) aren't allowed on deposit accounts, and banks take measures to prevent them (charging overdraft fees, blocking transactions, etc.).