Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.
Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again.
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.
A NOR gate can have two or more inputs. The o on the output means not showing that it is a Not OR gate. The output of a NOR gate is true when none of its inputs are true.