You will not interact with the USB device. The USB device should provide drivers that will create a virtual serial device in
/dev/ when you plug in your device. Once the device is plugged in and the driver has created the virtual serial device, communication takes place over the callout device file
/dev/xxx.cu or the TTY device file
xxx is particular to your driver). Communication might be as simple as
catting a text file with
stdout redirected to that path. Failing that, a serial-aware interface such as those mentioned by CharlesB might be necessary. If you are looking for a command line tool, try
socat, which has flags to configure the baudrate, parity, and bitwidth of messages sent across a serial port.