It would be something similar to
top, where you see your cpu processes in real time. I'm not looking for a GUI like Wireshark to do it.
Those give all detailed info in a ui-style. If you are looking for a much simplier one use:
You'll get something like (realtime updates):
[user@host ~]$ vnstat -l Monitoring em1... (press CTRL-C to stop) rx: 4 kbit/s 5 p/s tx: 4 kbit/s 3 p/s
The same command can be used to get daily/monthly/etc traffic reports.