Become: trở thành + noun, trở nên + adjective

English "become" splits in two. Before a noun, use trở thành: Em muốn trở thành bác sĩ. I want to become a doctor. Before a describing word, use trở nên: Có con rồi, cuộc sống trở nên bận rộn hơn. Once you have kids, life gets busier.

Both sound a little careful. You'll hear them when someone tells a story or talks about plans, and you'll read them all the time in the news: Phở đã trở thành món ăn nổi tiếng khắp thế giới.

Relaxed talk has shorter ways. Before a noun, thành alone is enough: Hai đứa thành bạn thân từ hồi đi học. They became best friends back at school. With a describing word, Vietnamese usually adds ra, lên or đi after it instead: Dạo này chị ốm đi nhiều. You've got much thinner lately (in Hà Nội, gầy đi). That pattern has its own page.

For the job you want to do, làm also works: Lớn lên em muốn làm bác sĩ. When I grow up I want to be a doctor.