Professionals: nhà + field (nhà báo, nhà khoa học)

Put nhà before a field of work or study and you get the person who does it professionally: nhà báo (journalist, from báo, newspaper), nhà văn (writer), nhà thơ (poet), nhà khoa học (scientist), nhà thiết kế (designer), nhà đầu tư (investor). It's like English "-ist" or "-er", and it carries some respect: it's used for creative, expert or educated work.

Other jobs are built differently. Staff take viên at the end: nhân viên (employee), giáo viên (teacher). Skilled trades take thợ in front: thợ may (tailor), thợ sửa xe (mechanic). So nhà isn't used for a shop assistant or a cook.

Nhà still means "house, building", and many nhà words are places, not people: nhà hàng (restaurant), nhà sách (bookshop), nhà thuốc (pharmacy). The second word nearly always tells you which: a field of work or study makes a person; something sold or done there makes a place.

In conversation, people often say what someone does with làm: Chị Lan làm báo. Lan works as a journalist.