This is Bollinger band indicator. Default value is set at length 20 with 1 Standard Deviation (Narrow)
Upper and Lower Band is filled with blue color to indicate volatility of price movement
Line chart is represent price movement. Decision to buy/sell is as following :-
1 - Potential Buy - Price Line turned Green crossed above upper Band.
2 - Potential Sell - Price Line turned Red crossed below lower Band.
Note : Price breakout from narrow band normally result in rally.
The longer duration of narrow band will result in stronger rally after breakout
Note : Best use with "EMA Indicators with BUY sell Signal"