This is a two step process in Linux.
First, if needed (usually not for most common serial devices) set the speed. Most work fine at the default (9600 last time I looked), and you really only need to set speed of your trying to cram lots of data (i.e. a modem) or the device requires it. To set the speed you use stty to do that.
stty -speed 19200 -f /dev/something
Second you will have an eaiser time of you open two terminals one for input and one for output (though it's not "needed" it does make this a lit easier)
To read from the device (or any thing) you
cat /dev/something or better yet
cat -v < /dev/something give them both a try and see which you like better.
On the input side, to send to your device
echo -ne 'your gibberish here' > /dev/something should work just fine.
All your really doing is reading and writing to a "file". That's it.
For more info you can look at https://askubuntu.com/questions/411108/how-to-write-characters-to-serial-port or How to send data to a serial port and see any answer? and http://papers.mpastell.com/serial.pdf
Don't get discouraged. Sometimes it can be a bit rough coming from Windows to Linux. You expecting a complicated answer and it's usually quite simple.