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.
An EX-OR gate can only have two inputs. The output of an EX-OR gate is true when its inputs are different (one true, one false).
Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.