This is the 239th most frequent Ukrainian word.
почав
"Почав" means "started" or "began."
The word 'почав' here is used to denote the beginning of an action, specifically starting to read.
Він почав читати книгу.
He started reading a book.
'Почав' indicates the initiation of a subsequent action in response to an event, showing cause-effect.
Коли пішов дощ, він почав бігти додому.
When it started raining, he began running home.
This usage of 'почав' introduces the context in which an activity starts, highlighting the manner or method of commencement.