The body spans the open and the close, filled or coloured to show which came first, and the wicks reach to the high and the low. One mark therefore carries four prices and the direction of travel between them.
The shape is a summary of who won the period. A long upper wick on a small body says buyers pushed price up and could not hold it. A wide body with almost no wicks says one side controlled the whole period without being challenged.
Named patterns such as the hammer, the engulfing candle and the doji are widely published and correspondingly widely front-run. They carry more weight at a level that already matters, such as a prior high or a moving average, than they do in the middle of a range.