How do you connect the arduino to the roborio using the digital pins?

Hi, How am I able to communicate with the arduino from the roborio? I know how to read the data on the arduino but i am not sure how to send data using the roborio, I code in java, i want to be able to push a button on the controller and it sets a digital pin to high and then read it on the arduino, how would I wire it and program it?

The RoboRIO can communicate with the Arduino in many ways. Our team uses I2C because we have a relatively complex communication protocol between them. We used the Arduino to control an LED matrix message board and the RoboRio will send text messages and parameters to the Arduino for displaying on the LED message board.
It sounds like your scenario is much simpler. In your case, you can connect one of the digital pins of the RoboRio to one of the digital pins on the Arduino. Then program the digital pin on the RoboRio as a digital output and the digital pin on the Arduino as a digital input. To program the RoboRio to set the digital output pin high or low, use the DigitalOutput class in WPILib.