If you expect the market go bullish, you can buy long to profit from price rising. For example, you buy a share of stock at $100 and close position or sell the stock at $120, then you make $20 dollars cash.
If you expect the market go bearish, you can sell short to profit from price falling. For example, you borrow a share of stock from a security dealer and sell it for $100 in cash. When the stock price falls to $80 dollars, you buy back the stock and return it to the lender, and you make $20.