Answer first, then check. Getting one wrong and reading why is worth more than getting five right.
Every explanation names the page that teaches the answer, and the glossary covers any term you meet here before you have read its page.
Mixed set
The full transaction flow
Who does what
By topic
Roles
Lifecycle
Authorization
Capture
Voids, reversals, and refunds
Clearing and settlement
Funding and disbursement
Disputes and chargebacks
Timing
Cards
ACH