candlestick represents 15 minutes of price movement.

A green candle tells us that the price went up during these 15 minutes whilst a red candle tells us that the price went down during the 15 minutes. The open of a green candle is where the price started to form. Let’s say this candlestick started to form at 9:00 oclock then the opening price is at 9:00 whereas the close will be at 9:15 where the candlestick finished its movement. The low represents the lowest point the price was fluctuating during the 15 min period and the high the highest price the candle reached during the 15 min period. Notice here that a green candle has its open below while a red candle has its open price up and close price down since red represents a price decline and green a price incline.
If you are on a one hour chart everything stays the same except the open price will be at 9 and closing price will be at 10.