A simple way to use it is to leave the base connection open. Connect the collector and emitter to a load (for example, ground the emitter and connect a 10k resistor from the collector to a positve power supply, like +5 volts for us old timers), and then on the input side, drive the LED with 10 millamps (ground the cathode, and connect a 330 ohms from a 5 volt power supply to the anode).
Whenever you drive the LED, the collector will go to ground. It will be very close to +5V the rest of the time.