I often find говорить equated with "speak" and сказать equated with "say". But if I am correct, this is misleading. I believe that the (primary? only?) difference between говорить and сказать is that the former is an imperfective verb and the latter is a perfective verb. By contrast, there is no such aspectual difference between "speak" and "say", but they differ in terms of whether they specify the conveying of information. "Speak" is generally intransitive and refers to the act of producing words, rather than conveying information:
Did you speak with her? (intransitive)
I never speak when I'm in a group. (intransitive)
though there are two main exceptions where it is transitive:
I speak Hungarian. (or any other language; here "speak" is grammatically transitive, but focuses more on utterance than conveying information)
You speak the truth. (rather rare/literary; note that here it does refer to the exchange of information, but similarly focuses more on utterance than on conveying information)
By contrast, "say" is always transitive (except in the fixed expression "You don't say") and always is about conveying information:
I didn't say anything.
The verb "tell" is generally not mentioned in these discussions, but I think it should be. Grammatically speaking, "tell" can be transitive or intransitive, but semantically, it's always about conveying information, whether or not that information appears in the sentence:
I told my mother immediately. (intransitive, but refers to a particular piece of information)
I would never tell him something like that. (transitive)
In Russian, I think that говорить and сказать can both emphasize either the act of uttering words or the act of conveying information. Is this right?