Resistors resist the flow of electrons, hence the name. They can be used in to limit the current flow, such as current limiters for LEDs. The amount of current that flows through a resistor is proportional to the voltage applied. 1 volt applied across a 1Ω resistor will allow 1 amp of current to flow.
Resistors may be used in voltage divider circuits to permit different voltages to be derived from a single voltage source. They may be used for current limiting, as mentioned earlier. They are labeled and used according to their resistance in ohms (Ω).
A capacitor stores electrical energy in an electric field. Capacitors have two conductive plates, with an insulator between. Applying a voltage to the capacitor causes electrons to flow into one plate and other electrons to flow out of the other plate, all driven by the applied voltage, creating an electric field in the insulator between the plates. The current does not pass through the capacitor, because the insulator prevents it. When a circuit is made between the two plates, the electric field collapses, generating current flow in the opposite direction from the charge current.
Capacitors are used for filtering power by removing the ripple from rectified AC, or as DC blockers. In the case of blocking capacitors, the applied voltage may be large with a smaller alternating signal riding on it. The capacitor will allow the alternating signal through while blocking the steady part of the voltage.
Capacitors are labeled and used according to their capacitance in farads (F). Since a farad is such a large unit, capacitors are generally rated in picofarads (pF or billionths of a farad) or microfarads (µF or millionths of a farad).
An inductor is typically a coil of wire, but may be just a single straight conductor. The inductor resists changes in the current flowing through it. If you apply a voltage across it, current will slowly rise until it reaches the value it would have were there no inductance. It does this because the current flow is storing energy in a magnetic field. If you remove the applied voltage, the inductor will attempt to maintain the current flow as the magnetic field collapses, generating current in the wire.
Inductors are also used to filter ripple, by preventing the current flow from changing. They are used in frequency determining circuits, called tank circuits or tuned circuits, especially in radio devices. Inductors are labeled and used according to their inductance in henries (H). Since henries are very large, inductors are typically rated in millhenries (mH or thousandths of a henry) or microhenries (µH or millionths of a henry).