Nothing but: toàn (là)

Toàn before a noun means "all" or "nothing but": everything in the group is the same kind. Là often comes between, with no change in meaning: Trong tủ lạnh toàn là bia. There's nothing but beer in the fridge. Lớp em toàn người nước ngoài. My class is all foreigners.

Like "nothing but" in English, it often carries surprise or a mild complaint: Tối nào cũng toàn mì gói. It's instant noodles every single night.

Before a verb, toàn means "always" or "only ever": Anh ấy toàn nói chuyện công việc. He only ever talks about work. Em toàn đi xe buýt. I always take the bus.

For emphasis, the noun can be said twice with là between: Chợ Tết đông lắm, toàn người là người. The Tết market is packed, people everywhere.

In news and official writing, toàn before a few words means "the entire": toàn quốc (nationwide), toàn thế giới (the whole world). That's a different, formal use; this one is everyday, and it's about what something is full of.