Why map Arduino pins 2 and 3 to Rx and Tx instead of using the build in Rx and Tx pins?
SoftwareSerial lets you add an additional serial port using "bit banging" to read/write to the port. This lets you connect up another serial device (eg. GPS, RFID reader, MIDI device, LCD) to this extra port, and still use the hardware serial interface (pins 0 and 1) via the USB port to send messages and/or debugging to the connected PC.




  Is there any special wiring needed to send messages to the connected PC? Or is it enough that they just not be in use?


Pins 0 and 1 are connected to the Atmega16U2 USB interface chip. If it gets what looks like serial data it will forward it to the PC.