Bands are calculated with the std error and variance of the price actions. So if price cross up or cross down the variance bands, you could expect a reversal movement.
So if price cross up with the bands and after that there is a reversal candle movement, a short position could be taken.
If price cross down to the bands and after that there is a reversal candle movement, a long positon could be taken.
All risk management and money management is up to you.