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).
A capacitor stores electric charge. Polarised capacitors must be connected the correct way round. They usually have larger values, 1µF and greater. See above for uses.
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.