This is the 4766th most frequent Russian word.
заняться
"Заняться" means "to take up," "to engage in," or "to start doing something."
In this sentence, 'заняться' means 'to take up' or 'to engage in', indicating the start of an activity.
Я решил заняться спортом для улучшения здоровья.
I decided to take up sports to improve my health.
Here, 'заняться' denotes engaging in a leisurely activity, implying pursuing something enjoyable.
В свободное время я люблю заняться чтением книг.
In my free time, I like to engage in reading books.
In this usage, 'заняться' is employed to indicate attending to or dealing with a necessary task or duty.