1. Introduction:

Bollinger Bands are a volatility based indicator, developed by John Bollinger, which have a number of trading applications.
There are three lines that compose Bollinger Bands: A simple moving average (middle band) and an upper and lower band. These bands move with the price, widening or narrowing as volatility increases or decreases, respectively. The position of the bands and how the price acts in relation to the bands provides information about how strong the trend is and potential bottom or topping signals.
Bollinger Bands are used on all time frames, such as daily, hourly or five-minute charts. Bollinger Bands have two adjustable settings: the Period and the Standard Deviation. The Period is how many price bars are included in the Bollinger Band calculation. The number of periods used is often 20, but is adjusted to suit various trading styles.
2. what is consists of ? :

The Standard Deviation is typically set at 2.0, and determines the widths of the Bands. The higher the Standard Deviation, the harder it will be for the price to reach the upper or lower band. The lower the Standard Deviation the easier it is for price to “breakout” of the Bands.
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