The diference of using Say,Speak, tell

Say / tell

We use: tell + somebody.

I told David about it.
Did you tell him?
He told me that he was ill.

We use: say + clause. 
We use: tell + clause when we include a pronoun such as me, him, us, etc.

She said she was ill.
She told him she was ill.

We use: say + something + to somebody.

She said hello to me.

We use tell when we are giving facts or information:
tell somebody (that) ...
tell somebody something
tell somebody about something
tell somebody who/when/where.

She told me (that) she was ill.
She told me the news.
Tell me about your new job.
He told me where it was.

Speak / talk

Speak and talk have similar meanings. They suggest that a person is using his or her voice, or that two or more people are having a discussion.

We can say:
speak to somebody 
talk to somebody 

speak to somebody about something
talk to somebody about something

How old were you when you learned to speak?

What are you talking about?

Who were you speaking to on the phone?

Who were you talking to on the phone? 

I was speaking to Mark about cricket.

But we say:
speak a language NOT talk a language
talk nonsense NOT speak nonsense.
Speak to and talk to are used more often thanspeak with and talk with.

He speaks four languages.
Stop talking nonsense!
I was talking to Tom yesterday.

Speak is a little more formal than talk, and is often used in polite requests.

Hello, could I speak to Mr Jones, please?