A candlestick is a way of charting one trading session's price behaviour in a single shape. Each candle has a body, showing the range between the opening and closing price, and often thin lines above and below called wicks (or shadows), marking the session's high and low. If the close was above the open, the body is typically shown in one colour (often green); if the close was below the open, it's shown in another (often red). A row of candles side by side, one per session, forms a candlestick chart — the same underlying open/high/low/close data as an ordinary line chart, just displayed with more structure per period.
Certain recurring candle shapes are commonly given names and interpretations by chart readers, though every one of them is a description of what already happened in a session, not a prediction of what happens next.
A doji has a very small or nonexistent body — the open and close were close to or the same as each other, with the session's price otherwise moving in both directions before settling near where it started. It's commonly read as a session where demand and supply were roughly balanced, without a clear direction winning out.
A hammer has a small body near the top of the session's range, with a long lower wick and little or no upper wick — the price fell well below the open at some point during the session before recovering to close near it. A shooting star is close to the mirror image: a small body near the bottom of the range with a long upper wick, meaning the price rose well above the open before falling back by the close.
An engulfing pattern spans two candles: the second candle's body fully covers the first candle's body in the opposite direction — a large candle in one direction immediately following a smaller candle in the other. It's commonly read as a sign that whichever side (demand or supply) was dominant in the first session lost ground abruptly in the second.
Candlestick patterns describe shape, not certainty — the same shape can appear in very different contexts (a strong trend, a narrow trading range, around a results announcement) and chart readers commonly weigh a pattern together with other context, such as trading volume or where it appears relative to recent highs and lows, rather than reading a single candle in isolation.