This is the 1586th most frequent Russian word.
совершил
"Совершил" means "committed" or "performed."
The word "совершил" here is used to express that he has performed the action of making an error.
Он совершил ошибку.
He made a mistake.
The word "совершила" here is used to denote the action of carrying out a heroic deed.
Она совершила подвиг.
She accomplished a feat.
The word "совершили" is utilized here to convey the action of completing a journey.