‘Say’ or ‘tell’?

We use tell with an object (i.e., who is to be told):

•    Can you tell me where he has gone?

Also, we use tell to mean to instruct or to inform:

• I told her to wait at home until I get there. (instructing)
• He told us about his experiences of teaching English in a foreign country. (informing)

Say can be used for any kind of talking, and does not generally need an object (i.e., you do not need to indicate who is being told):

• She said she might drop in for a few hours this weekend.
• Can you please say that again?

If you use an object after say, you must use to with the object:

• He said goodbye to his children and walked out the door without turning back.