Speak, talk, tell, say

Say - express something with words.
Tell - means to give information to a person.
Speak = Talk – exchange information with somebody.
* speak languges

Examples
“Where are they going? She didn’t say.”
“Where are they going? She didn’t tell me.” (She didn’t give me the information)
“What did he say?”
“What did he tell you?” (what information did he give you?)
“Say ‘hi’ to Paul for me!”
“Tell Paul I said hi!”
“I want to say something about our teacher.”
“I want to tell you something about our teacher.”