Uses Examples
Say used with direct and indirect speech
Say is most often used without a personal object.
If we want to put a personal object after say, we use to.
She said that it was my last chance.
He said, ‘Good morning.’
She said that she would be late. (not She said me...)
And I say to all the people of this great country...
Tell used with direct and indirect speech
after tell, we usually say who is told, i.e., tell someone something
only used to mean ‘instruct’ or ‘inform’
Tell is used to tellsomeone to do something
Tell is not used before objects like a word, a name, a sentence, a phrase.
We do not usually use itafter tell to refer to a fact.
tell someone again (repeat)
She told me that she would be late.
She told me that it was my last chance.
(not He told them, ‘Good morning.’)
Tom’s mother told him to clean his room.
Alice said a naughty word...
(not Alice told a naughty word...)
‘I’ll tell you tomorrow.’ (not I’ll tell you ittomorrow.)
‘I don’t want to tell youagain to get your homework done.’
Talk There is not very much difference between speak and talk.
Talk is the more usual word to refer to conversational exchangesand informal communication.
When she walked into the room everybody stopped talking.
Speak is often used for one-way communication and for exchanges in more serious or formal situations.
Speak is the usual word to refer to knowledge and use of languages.
I’ll have to speak to that boy -- he’s getting very lazy.
After she had finished reading the letter, nobody spoke.
She speaks three languages fluently.

say, tell, talk, speak 이 단어들은 모두 말을 한다는 점에서는 같지만, 실제로 쓰임세가 다르다
자세한건 위 표를 보면 알 수 있을테지만, 간단히 핵심만 말해주자면 이렇다.

say : 대상이 없이 말하다, "~라고 말하다" 정도의 의미

tell : 대상에게 말하다, 말을 전하다, 이야기 하다

talk : 사적으로 말하다, 수다 떨다

speak : 공식적으로 말하다, 연설하다