SAY and TELL in Reported speech

Statements 

Say and tell are the two verbs most commonly used to report statements in English. We can use either say or tell to do this.

she told me… / she said…

The main difference is that when we use told we normally say who is spoken to, so we have to use it with a direct personal object. When we use say, we don’t normally indicate who is spoken to, or, if we do, we must put to before the object. Compare the following:

He told me that he was going into hospital for a major operation.
He said that he expected to be kept in for about six weeks.

Did you say anything to her?
I told her nothing about it!

Note that when we are quoting direct speech, say is the more commonly used verb as say refers to any kind of speech. Tell is used only with the meaning of instruct or inform. Compare the following:

“You don’t look too happy,” I said.
“I get really stressed at work,” she said.
“Eat properly, exercise regularly and get eight hours’ sleep each night,” I said.
“Eat properly, exercise regularly and get eight hours’ sleep each night,” I told her.

Note that we can use many other more informative reporting verbs, in addition to said, to report statements and in quoting direct speech:

The shoe shop manager explained / insisted that I couldn’t exchange the boots or get my money back as I’d had them for over a month. I had to admit that they no longer looked quite new.

“You don’t look very happy,” I remarked.
“I get really stressed at work,” she confessed.
“Eat sensibly, exercise regularly and sleep for eight hours each night,” I advised her.

If we use inform, warn or instruct, advise or teach as alternatives to tell, we have to remember to use them with a direct personal object:

They informed me that they wouldn’t be sitting the IELTS test after all.
I warned him that he would be disqualified if he cheated in the exam.
She taught me everything I know.

told + object + infinitive

We can also use the object + infinitive pattern with told and other verbs suggesting commands or orders. We cannot use said in this way:

I warned her not to stay out after dark in this area as it isn’t safe.
I told her to get a taxi from the station and not to walk.

told + object + about

Note that if we are reporting the topic and not what was actually said, we use this construction. Again, it is not possible with said:

They told me all about their holiday in Greece.
I told them about how I got sunburnt in Portugal.

Reporting questions

Note that we do not use say or tell to report questions. 
Instead we must use ask with if or whether to report yes/no questions and with the question word for all other types of questions. We normally, but not always, use ask with a direct personal object when reporting questions in this way:

She asked me if I was going to Dee’s party.
I asked her whether Joan would be coming.
She asked what clothes I would be wearing.
I asked where I should meet her.

asked + object + to / about

Like told, we can use asked with to + infinitive or about + topic:

I asked them to turn down the volume on the CD player as I couldn’t concentrate on what I was reading. They asked me to move to another room.

I asked them about the holidays they had enjoyed in Greece and Portugal.

Source:bbc.co.uk