5. Negation

• don't / doesn't + verb (present simple):
  I don't know. He doesn't like coffee.
• isn't / aren't (with to be):
  It isn't cold today. They aren't home.
• didn't + verb (past, any subject):
  We didn't go there.

Cheat: only ONE negative word per sentence in English — 'I don't know nothing' is wrong, say 'I don't know anything.'