You need the driver for the cable and then a program to make use of the cable.
I have one myself, and I make it work in this way -
You need the module ps2303 added into the kernel to make the USB->Serial cable work.
I have this configuration to make the program minicom to allow me to easily connect to whatever the cable is plugged into:
jim@jimsworktop:~$ cat /etc/minicom/minirc.dfl
# Machine-generated file - use "minicom -s" to change parameters.
pu port /dev/ttyUSB0
pu baudrate 9600
Just typing minicom in the terminal allows me to connect.