[CentOS] Need to test serial port connection

I recently bought a new UPS, and I'm attempting to use nut to  monitor it.  
Following setup instructions everything seemed to go well until it came to 
testing the connection, which failed.

There is just one serial connector on the computer, so I set it to 
monitor /dev/ttyS0.   Either that is wrong, or communication is failing.  
I've been told to try minicom to monitor it, but I'm not familiar with 
minicom (or any similar app), so again, I may be wrong in the way I'm trying 
to use that.  I was told that unconnecting the device, then re-connecting it 
should give me a raft of output to the terminal - I saw nothing.

Could someone please give me idiot-level instructions on how to tell whether 
I'm connecting to the correct port, or whatever other information I need?

Thanks

Anne