If you hold stocks and want protection against a fall, you sell futures (a short hedge). If you plan to buy stocks later and want protection against a rise, you buy futures (a long hedge). Buying put options is another way to protect against a fall.
Consider a hypothetical example in which a stock index is at 20,000. An investor holding 200 million yen of stocks sells 10 futures contracts at 20,000, each with a contract unit of 1,000 times the index. If the stocks and the futures move in the same proportion as the index, the 20 million yen loss on the stocks when the index falls to 18,000 is offset by a 20 million yen gain on the futures. When the index rises to 22,000, the gain on the stocks is canceled by the loss on the futures.