Arduino works as a virtual serial port, so one end of the USB cable goes in the USB port on the Arduini board, the other end goes to a USB port on the PC.
When (and only when) Arduino is plugged in to the PC's USB port you will see a new serial port on the PC, this is the port your VB program should communicate with.
For this to work you must have installed the FTDI drivers for the virtual serial port, but if you can program the Arduino board from the Arduino IDE then the drivers should already be there.