Earphone A transducer which converts electrical energy to sound.
Transistor PNP 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.
Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again.
Diode A device which allows current to flow in only one direction.