how to code an analog signal

i am getting an analog signal ( varying ampere ) i need to get this signal into arduino to writ coding how to do that, as example i will get a signal ranging from 1micro ampere to 1200 micro amphere

The first thing to do is to turn the current into a voltage which can then be read by the Arduino.

Google is your friend... http://www.vwlowen.co.uk/arduino/current/current.htm