This is the 1555th most frequent Japanese word.
働く
"働く" means "to work."
In this sentence, 働く is used to denote being engaged in labor or work, specifically within an occupational context.
彼は毎日8時間働いています。
He works 8 hours every day.
Here, 働く reflects the act of engaging in activities that involve effort or service, in this case in a non-paid or voluntary capacity.
ボランティアとして働くのはとても充実感があります。
Working as a volunteer is very fulfilling.
In this example, 働く is used metaphorically to describe the operational functioning or activity of a machine.