Taking a "long" position in the stock market is when an investor buys a stock expecting that the price will rise so that it can be sold for a profit. Investors who go "long" are referred to as "bulls" or being "bullish" on the market. They believe stock value will keep charging in an upward direction. So shares bought at lower prices today can be sold at higher prices in the future.
Taking a "short" position in the stock market is when an investor sells stock shares that he or she does not own. Shares for the sale are borrowed from a broker and are returned to the broker at a future point in time. Short investors are referred to as "bears" or as being "bearish" on a stock or on the entire market because they believe stock price(s) will go down. Thus if shares are shorted (borrowed) at today's prices then bought and returned at a future lower price then a profit will be realized.
Either of the two trading strategies above can be used to make profits. The simple trick is to go "long" on stocks that truly will rise in price and short stocks that will truly fall in price. This concept is simple but not easy. How can you tell whether/when a stock will rise or fall? Usually there are indicators that can show which way a stock's price is likely to go. Since the investors that make up the stock market are sometimes irrational in their buying and selling habits no indicator is 100% successful all the time. But a combination of indicators can be used to raise the confidence level for a long or short trading decision.
Stock price is determined by investor sentiment and interest. The Ciation Investor Solutions metrics that measure price action, investor interest, and sentiment are shown below.