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.
A NAND gate can have two or more inputs. The o on the output means not showing that it is a Not AND gate. The output of a NAND gate is true unless all its inputs are true.
Voltmeter Measures voltage. The proper name for voltage is potential difference but voltage is more widely used.
Diode A device which allows current to flow in only one direction.