Your first goal should be to get a serial port up and running - Follow Salem's link. Or
Serial Communication With C Programming - C And C++ | Dream.In.Code
I use a USB/RS232 converter for this sort of thing - (Although I did see a second option - TCP connection in the C# link (?) Is that something that your printer is capable of? There is a lot out there for TCP, so that is a very good option if it has it)
Because you are using hardware directly from code (COM port or TCP) you are going to use non portable code. My advice if you wanted to port it to different systems is to keep that code in a different source file.
Once you have comms working, start with a "hello world" to the printer
After that is happening, you can start experimenting with different things such as bar codes...