Firefly III has several types of accounts. This goes beyond your own bank accounts and credit cards; there's more to finance than those two. There are three kinds of accounts in Firefly III.
These different account types exist because my Googling into accounting has learned me that you should split these up. Internally too, even accounts with the same name but different types are split up. For example, if you shop at the place you work at, you will have a revenue account called "Albert Heijn" from which your salary is drawn but also an expense account called "Albert Heijn" where you pay your groceries.
Asset accounts are normal bank accounts. They hold your own money. Your bank account is an asset account. Your savings account is an asset account. They would be called "Savings account" or "Checking account". These accounts can be created with an initial (negative) balance, which is useful since you won't be entering your entire financial history.
Asset accounts come in three flavours:
This is the default kind of asset account.
Shared asset accounts are shared with a partner, roommate or spouse. Use this to indicate that both (all) of you have access to this account. In Firefly III itself, you won't be able to actually share access between accounts, so this indication is purely for you.
Used to indicate the asset account belongs to a credit card. Firefly III does not (yet) respond to this, it's just for your administration.
When you spend money, you do so at a store, online or maybe using cash. Each of these places gets its own expense account.
Cash money is different though. When you withdraw money from an ATM and register it in Firefly III, don't register an expense account. Leave the field empty. This will make Firefly III fall back to a specially designed "cash account".
Likewise, if you deposit cash into an asset account, don't mention a revenue account (see below).
Another type of account is the revenue account. A revenue account belongs to anyone or any company that sends you money. These may be your employer, parents or friends. Possibly these are clients or the government.
Firefly III supports liabilities such as debts and loans, that you can track using Firefly III.