tell you what
Meaning
tell you what
(colloquial) Introduces a compromise or arrangement where the interlocutor has some benefit or advantage.
Examples
The best books... are those that tell you what you know already.
Tell me what you eat, and I will tell you what you are.
If you don't know how to die, don't worry; Nature will tell you what to do on the spot, fully and adequately. She will do this job perfectly for you; don't bother your head about it.
Children will tell you what they do, men what they think and older people what they have seen and heard.
Tell me with whom you go and i'll tell you what you are.
Tell me what you want to buy and I will tell you what you are.