Resistors are used to regulate the amount of current flowing in a circuit- the higher the resistor’s value or resistance, the less current that flows and vice-versa. Resistors values are measured in ohms (Ω) and are identified by the colour bands on their bodies. They may be connected into a circuit either way around (i.e., they are not polarised).
Resistors are made in different sizes, capable of dissipating or ‘getting rid of’ different amounts of energy (as heat). They are also made using different materials as the actual resistive element. Small low power resistors usually have an element made from either carbon or a thin film of metal. Larger resistors made to dissipate more power generally have an element wound from a wire such as nichrome (nickel-chromium alloy).
Symbol of a resistor:

Diagram of a resistor:

Polyester capacitor
Polyester capacitors use polyester plastic film as their insulating dielectric. Some polyester capacitors are called green caps since they are coated on the outside with green (or brown!) plastic to keep out dust and moisture. Their values are specified in microfarads (µF) , nanofarads (nF) or picofarads (pF), and range from 1nF up to about 10 µF. They are not polarised.
Symbol of polyester capacitor:

Picture of a polyester capacitor:

Electrolytic capacitor
Electrolytic capacitors (or ‘electros’) use a very thin film of metal oxide as their dielectric, which allows them to provide a large amount of capacitance in a very small volume. They range in value from about 100nF up to hundreds of thousands of microfarads (µF). They are commonly used to filter power supply rails, for coupling audio signals and in timing circuits. All electrolytic capacitors allow a very small DC ‘leakage’ current through them, but special ‘low leakage’ types are made so that this leakage current is much smaller than normal.
Note that electrolytic capacitors are polarised and the positive and negative leads are clearly...