All computer systems use Inputs, Processes and Outputs. In terms of your EV3 Robot:
An Input puts Information into the Brick e.g. the Colour Sensor tells the Brick when there is a Black line on the floor.
A Process could be a piece of programming that says when your Robot sees a Black line on the floor, stop moving forwards.
The Output in this case would be that the Motors driving the wheels would stop turning.
EV3 Brick and the Input (sensors) and Output Devices that can be plugged into it.