Do an online search with these keywords: difference say tell speak talk You'll find plenty of pages and forums which explain the difference clearly. :)

These are a few ways to differentiate between say/tell/speak/talk I want to 'tell' you something. What do you think we should 'talk' about? Do you 'speak' English? I would like to 'speak' on discrimination. Do you have anything to 'say'? Depends on what you want to express, if you are asking a question or addressing someone.