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).
An EX-NOR gate can only have two inputs. The o on the output means not showing that it is a Not EX-OR gate. The output of an EX-NOR gate is true when its inputs are the same (both true or both false).
An OR gate can have two or more inputs. The output of an OR gate is true when at least one of its inputs is true.
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.