The LED will flash whenever the IR Receiver picks up an IR signal. Connect a resistor to the "signal out" leg of the IR Receiver. The other end of the resistor goes into the negative/cathode leg of the LED. The other end of the LED needs to connect to power.

Three ways to recognize polarity of an LED:

1. The shorter leg is the negative/cathode leg

2. The head of the LED is flat on the side that is the negative/cathode side.

3. Inside the head of the LED, the larger metal piece is the negative/cathode side.

Further reading:

https://learn.sparkfun.com/tutorials/polarity/diod...