What the bands show
Bollinger Bands consist of a moving average in the middle and two outer bands placed a certain number of standard deviations above and below it. Because standard deviation measures how spread out recent prices are, the bands widen when volatility rises and narrow when it falls.
This makes them a visual gauge of volatility. When the bands squeeze tight, the market has been calm; when they flare wide, it has been moving sharply. Price spends most of its time within the bands, poking outside them during stronger moves.
The touch that is not a signal
A frequent beginner error is treating a touch of the upper band as "sell" and a touch of the lower band as "buy". In a strong trend, price can ride along a band for a long stretch, so blindly fading every touch is a fast way to lose money against a persistent move.
Touching a band means price has moved a notable distance from its recent average — nothing more. Whether that stretch snaps back or continues depends on context the bands themselves cannot tell you. The bands describe volatility; they do not predict reversals.
A more honest reading
Some traders watch a "squeeze" — a period of very narrow bands — as a hint that a bigger move may follow once volatility returns, though the direction is not indicated. Others use the middle average as a reference. These are contextual uses, not signals to trade on alone.
As with every indicator, Bollinger Bands are a lens for viewing volatility, not a source of predictions. They pair best with clear risk management and an acceptance that low volatility can persist and high volatility can strike without warning. No band configuration hides an edge that survives on its own.