The hammer is a bullish reversal pattern found at the end of a downtrend. It is a single candle pattern consisting on a candle with a short body with a long lower wick but a short or ideally no upper wick. This is seen as a reversal pattern as the sellers tried to push the market lower but the buyer gained control driving the prices close to the opening price.
The hanging man is a bearish reversal pattern found at the end of an uptrend. Also a single candle pattern but this time it also has a short or no upper wick but with a long lower wick. Showing the sellers are gaining control of the price causing it to drop.