Red candles show the price action and remember, the red candles mean that there was more selling pressure than buying pressure at the end of the session.
The candle SIZE is just the fluctuation of the market prices within that time window (say 30min or 1hr).
Lower shadow shows how low the price went during the session, with buyers buying up the lower prices. LONGER lower shadow = more sellers
The LONGER then shadow, the MORE volatility in the session.