Need help to commincate with COM port on the BeagleBoard Black

Hi all,

I’m a beaglebone newbie and i need help for my project.

I would communicate on an IHM with my beagleboard black by port COM , i have a little electronic card than have port COM and it connected on my beagleboard by the port USB.
In first i would make light led on the IHM for beginning, i would programming that with the C language and i need to work with linux on the beagleboard.

So i have see example here:

but its not really what i want , i would communicate with an ihm by port COM, i need help because i never work with beagleboard only with arduino uno and i dont no how i can make light on the IHM
with the help of the beagleboard by the port COM.