Please help me.Thank you!

To speak and to talk are very similar: both mean "to say something" or, in some cases, "to have a conversation." These verbs emphasize the act of saying something.

To tell is slightly different: it means "to convey information." This verb usually emphasizes not the act of saying something but the actual words that are being said.

This is why, in English, we say "Tell him I said hello"; we do not say, "Speak him I said hello" or "Talk him I said hello." Inversely, we say "I will talk with him" or "I will speak with him"; we do not say, "I will tell with him."