Members and staff: word + viên (nhân viên, hội viên)

Viên at the end of a word makes a person who belongs to a group or holds a role, often as staff: nhân viên (employee, staff member), giáo viên (teacher), sinh viên (university student), thành viên (member), hội viên (club member), diễn viên (actor), hướng dẫn viên (tour guide), tiếp viên (flight attendant).

You can't add it to any word you like; these are set words, many from Chinese. But viên at the end tells you it's a person in a role. Many take a second word for the kind of work: nhân viên ngân hàng (bank employee), nhân viên bán hàng (sales assistant).

Nhà comes before the field and names a respected profession: nhà báo, nhà văn. Viên comes after and names a member or someone doing a job; it's neutral and everyday. Trưởng names the head.

Like other job words, these take no classifier after a number: ba sinh viên, hai nhân viên.

Viên is also a classifier, for pills and small round things: một viên thuốc. In the news it sometimes comes before a person, viên cảnh sát; that sounds cold, so don't use it for anyone you know.