Indefinite pronouns
Negative form of the sentence: He told us something about his trip.
He told us nothing about his trip. / He didn't tell us anything about his trip.
Affirmative form of the sentence: He doesn’t know anything about the plan.
He knows something about the plan.
Negative form of the sentence: There is someone at the door.
There is no one/nobody at the door. / There isn't anyone/anybody at the door.