What is the difference between "since" and "for"?

Both describe time, but they answer different questions:

• "For" answers "how long?" — use it with a period/duration of time
  • "I have lived here for five years."
  • "She waited for two hours."
• "Since" answers "from when?" — use it with a specific point in time
  • "I have lived here since 2019."
  • "She has been waiting since noon."

Quick test:

• Can you replace it with "for a period of"? → Use for
• Can you replace it with "starting from the moment of"? → Use since