Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again.
Zener diode A zener diode can be used to maintain a fixed voltage.
Transistor NPN A transistor amplifies current and can be used with other components to make an amplifier or switching circuit. This symbol is for a bipolar junction transistor (BJT), the type you are most likely to use at first.
Microphone A transducer which converts sound to electrical energy.