English Grammar Reference: Differences between say and tell

We use say when we don't say who is being spoken to.

We use tell when we say who is being spoken to.

We can use say to specify who is being spoken to if we use say to although this is less common than tell.

say	I said I didn't know him. He said he was happy with his new job. It says in this paper that they are going to close the factory.
tell	I told her I didn't know him. He told his mother he was happy with his job. The owner of the factory told me they are going to close the factory.
say to	I said to her that I didn't know him. He said to his mother that he was happy with his job. The owner of the factory said to me that they are going to close the factory.