to clarify,saying screen i mean i have to get the adc outputs on the computer screen using the usb connection
So you need two pieces of code.
One that takes readings and passes them through the serial port. And the other on a computer that takes what is on the serial port and turns it into a graph.
What language are you going to do that second one in?
This sounds a lot like an arduino oscilloscope, google that for some examples.