Accessing USB Port in Visual C++

Usually the device manufacturer provides an API for interfacing the device with the PC (read the documentation). Very often (for low speed devices) they provide a serial port emulator, that is you communicate with the device using standard RS232 communication (again, check out your device documentation).

As about Windows API:
Windows is the Operative System, the API it provides are not only the ones used for 'the windows'. Specifically serial communication (USB included) functions are ready-to-use for console applications.


[update]
If you are using the FTDI chip a chip then (assuming the corrensponding driver is installed on your PC) you use standard RS232 API for communicating with it (see for instance: "Using Communication Resources" at MSDN[^]) on the PC side.
On the other side you typically have a, hopefully, a microcontroller with UART device.
[/update]

To access USB devices you must talk with the device specific USB driver using a library provided by the device manufacturer (or the manufacturer of the used USB interface chip). Whithout knowledge about the used device, nobody may help you here.

Console applications can call Windows API functions (and most existing console applications do so). How would you access a file or a serial port from a console application without using API functions?

If you don't know much about interface programming and your device has a serial port, you may buy an USB-to-RS232 converter. Such converters provide a virtual serial port interface that can be accessed like a physical port.