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.
Light Emitting Diode A transducer which converts electrical energy to light. Usually abbreviated to LED.
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.
A capacitor stores electric charge. It can be used with a resistor in a timing circuit, for smoothing a supply (it provides a reservoir of charge) and can be used as a filter (blocking DC signals but passing AC signals). Unpolarised capacitors usually have small values, less than 1µF.