Hello Mathieu,
Once connected to a USB port on a computer with drivers installed the ICUSB23216FD, or other USB to serial adapters, will show up with COM ports or serial interfaces. This might vary a bit depending on your operating system.
RS-232 communication is very standardized, and while StarTech.com does not have specific support for C++ or have an SDK, I should certainly expect that that there are libraries available for serial communications. Once you have a C++ library imported it should allow you to control the serial devices. Sadly, I am not very familiar with C++ so I do not have any recommendations.
I hope that this information will at least point you in the right direction!