How to declare a serial device by USB connection on Arduino

Projects Interfacing w/ Software on the Computer
2

So may i know how to declare its baud rate,port,etc...on arduino?

Set the baud rate using Serial.begin(). The port is defined by which pins you connect to. The USB cable is connected, via a USB-to-serial chip, to pins 0 and 1 which are hardcoded to the Serial instance.