I am going to assume that you wish to communicate to some device connected to the serial port. You read and write to the serial port using VISA Read and VISA Write. These functions as well as a function to configure the serial port (baud rate, etc.) are on the Instrument I/O>Serial palette. You can also use the Instrument I/O Assistant. There are shipping examples on serial communication and if you go
here, you'll find links to tutorials and other examples. The only external hardware you need is a cable to your device and the device itself.
