Connecting the output from a function generator through a BNC cable to the input pins of a pcf8591

I am trying to work with the signals generated by a function generator using Raspberry Pi. Since Raspberry Pi does not have an inbuilt ADC, I used pcf8591. Now, I do not know how to feed the signal generated by the function generator into the input pins of pcf8591. Please help.

Check my PIC tutorials, which show an analogue connection board for a PIC - it applies just as well to a PCF8591.