This is the 17736th most frequent Russian word.
узнав
Having learned or recognized.
In this sentence, 'узнав' is a gerund derived from the verb 'узнать', meaning 'to learn' or 'to find out'. It specifies the circumstance under which the subject took an action.
Узнав о результатах экзамена, он сразу позвонил родителям.
Having learned about the exam results, he immediately called his parents.
Here, 'узнав' functions as a gerund explaining the cause of the subject's happiness.
Она была очень рада, узнав о его успехах.
She was very happy, having learned about his successes.
In this instance, 'узнав' is used to describe the action completed before the understanding occurred.