My understanding is that "telling" is a special case of "saying". "Saying" is just the uttering of words in the general case (although you can also say "the newspaper said ..." when of course it didn't utter anything). For example, "I said I was sorry". The verb "to say" is used when you don't want or need to convey that there was any particular purpose or direction to the utterance. "Telling" is the uttering of words with the intention of imparting information to a particular listener (or listeners). For example, "I told you I was sorry". The verb "to tell" is used when you DO want to convey that there was a particular purpose or direction or intention to the utterance. :)

Here is a rule to remember: -said/say + something -told/tell + somebody something for exemple: -You say something -She said to him: 'I am not feeling well. -You tell somebody something -She told him that she was feeling well

The difference is to do with what it is that is being expressed. 'Tell' implies information that is already known, in the past, that is now being recited. For instance you would 'tell a secret' or 'tell a story' or 'tell me how to use this machine'. It the kind of speech that repeats something to the listener. As such, it can be used in the imperative - for instance 'Tell me your name!' or 'Tell me the truth!'. Say' is more spontaneous, and applies to normal conversation between two people. Reported speech is always 'he said/she said', and not 'he told/she told'.