How do you use these devices? In the case of character devices, it can be quite simple:
Open the device as if it were a normal file, and read from or write to it.
$ cat document.txt > /dev/lp0
In a program, sending data to a device is
int fd = open ("/dev/lp0", O_WRONLY);
write (fd, buffer, buffer_length);
close (fd);
