Connecting a led
A LED must be connected around the correct way in a circuit and it must have a resistor to limit the current.
The LED in the first diagram does not illuminate because a red LED requires 1.7v and the cell only supplies 1.5v.
The LED in the second diagram is damaged because it requires 1.7v and the two cells supply 3v.
A resistor is needed to limit the current to about 25mA and also the voltage to 1.7v, as shown in the third diagram.
The fourth diagram is the circuit for layout #3 showing the symbol for the LED, resistor and battery and how the three are connected.
The LED in the fifth diagram does not work because it is around the wrong way.