Sending voltage according to database

Hi Guys,

Im a newbee on the arduino platform, for a new project I want use an input voltage to sending another output voltage.

For example I want to readout the voltage of a car system 10-14v, maybe with a resistor to make it below 5V (for arduino).

And with the input voltage, I want to send a way much lower voltage (dynamic).
Can someone help me with this project?

Thanks in advance

That's too vague a description to help really. Is the output voltage a function of the input voltage only?
Is it liner? Does it have state? What database?