Imagine a price chart like a little mountain range, with ups and downs. A green candle is like a bar on that chart that's colored green. A green candle means the price closed higher than it started at that time period (like a day or an hour). So, a green candle tells you that overall, people were buying more than selling during that time, which suggests some optimism about the price going up in the future. The wider the green body and the shorter the tail at the top, the stronger the buying pressure was.
