The whole, all of: cả

Cả before a noun means "the whole" or "all of": cả ngày (all day), cả tuần (the whole week), cả nhà (the whole family), cả lớp (the whole class). It takes the group, or the stretch of time, as one block.

Before a number it means all of that many: cả ba người (all three of them). Cả hai is "both": Cả hai đều đẹp. They're both nice. As there, đều often comes before the verb.

Tất cả also means "all", but it gathers separate things or people, tất cả các phòng (all the rooms), and it can stand on its own: Tất cả đều đồng ý. Everyone agreed. Cả can't stand alone like that. For a stretch of time or one whole thing, only cả works: cả ngày, never tất cả ngày.

Watch for cũng later in the sentence. Cả em cũng biết means "even I know"; that use, often with ngay in front, has its own page.