It helps to have two liquid tubes, in case you break one but still want to access your beer. Cut the liquid line with a pair of sharp scissors.
Insert the barbed connectors into the cut ends of the tubes and secure with hose clamps.
Thread the flow meter into the connectors (don't forget the teflon tape)-- now the liquid will go through the flow meter!
Run the extension wires out the back of the fridge so they can be hooked up to the RasPi/Arduino/system of your choice.