LEDs are small, low-power, easy-to-use light emitting components.
They have two leads, one of which is positive, the other negative. The negative lead is the shorter one, and the positive lead is longer. Also, there is a flat side to the base of the bulb which indicates the negative lead. If you connect an LED the wrong way round, it will not light up.
Lastly, LEDs must be connected to a resistor to stop too much current passing through them and burning them out. You can use equations calculate the ideal resistance to use, but in this workshop using any resistor between 100 and 500 Ohms will be good.