Each candle summarises one period of trading, for example one hour on the H1 chart.

The body

The thick part shows where price opened and closed. A green (or white) body closed above its open; a red (or black) body closed below.

The wicks

The thin lines show the highest and lowest price traded during the period. A long wick means price went there and was rejected.

What to look for

Long bodies show conviction. Long wicks at a support or resistance level show rejection. Small bodies after a strong move show hesitation. Most named patterns are just combinations of these three ideas.

Practical takeaway: a candle only means something in context. A rejection wick at a level you marked in advance is information; the same wick in the middle of nowhere is noise.