Say: nói, thốt ra điều gì
"I’m so tired",  He said.

Speak: nói, phát ra lời, sử dụng giọng
She spoke with an American accent.
Could you speak a little louder?
He speaks English.

Tell: nói, kể với ai, truyền đạt thông tin
She told me some funny stories about her husband.I will tell you my secret.

talk:  nói, nói chuyện, bàn về...
I spent a long time talking to him.
I want to talk with her.
I don't want to talk about money.