Firmata: A standard Arduino sketch that reads all of the Analog and Digital Pins from Arduino and reports them to software on your computer. This is a catch-all software and you don’t need to change it.
Serial: ‘The Serial library reads and writes data to and from external devices one byte at a time. It allows two computers (your Arduino and your computer for Ex.) to send and receive data.
Baud Rate: speed at which data is being sent across the serial port. I usually use 9600, which is pretty standard. How much this matters depends on balancing precision of reading your sensors with not wanting to crash your software.
Bytes: unit of digital information – serial data is sent in bytes.
* note that in Processing you may need to change which device is being read by changing the value in the brackets here (mine worked with 1 instead of 0): String portName = Serial.list();
Arduino and Processing: http://playground.arduino.cc/Interfacing/Processing
Processing and Serial: https://processing.org:8443/reference/libraries/serial/index.html