A Candle packages OHLC into a single shape you can read at a glance. Body, wick, colour — three pieces of information, all derivable from the same four numbers, presented so the eye can sweep across a chart and grasp the shape of the day without doing arithmetic.
The body
The body is the thick rectangle between the open and the Close. Its height shows how far price travelled, net, between the start and end of the bar. A tall body means decisive movement; a thin body means price ended roughly where it began even if it wandered in between.
Wicks
The thin lines above and below the body are the wicks (also called shadows). The top wick reaches up to the bar's high; the bottom wick reaches down to the low. A long wick says price went there but did not stay — the market visited that level and was pushed back. Wicks are the visual signature of rejection: where the buyers gave up, where the sellers gave up.
Colour
Convention varies, but on most platforms a green (or hollow, or white) candle means close > open — the bar ended higher than it began. Red (or filled, or black) means close < open — it ended lower. Colour is purely a function of those two numbers; it tells you nothing about volatility, range, or whether the move was meaningful. A green candle with a tiny body and huge upper wick is not a win for the bulls.
What one candle tells you
On its own, one candle is a sentence, not a paragraph. It tells you what happened inside one window of time — the open, the high, the low, the close, the colour. It does not tell you what happens next. Single-candle patterns (the doji, the hammer, the engulfing bar) are sometimes useful as context, but they are weak as standalone signals. Treat each candle as one data point in a longer story.
Réflexion
Pick a candle on any chart with an unusually long wick. What had to be true for that wick to exist? Walk yourself through the order of events that produced it.