The price movements of any stock are posted throughout the trading day and summarized at the end of the trading day. For example, April 2, 2019, shares of Apple Inc. (AAPL) opened at $191.09 and closed at $194.02. During the day, as indicated in the "day's range" listed to the right of the closing price, shares dropped as low as $191.05—the intraday low—and hit a peak of $194.46—the intraday high.
Trending stocks rarely move in a straight line, but instead in a step-like pattern. For example, a stock might go up for several days, followed by a few steps back during the next few days before heading north again. If several of these zig-zag patterns are strung together, and the chart appears to be moving higher with some degree of predictability, the stock is said to be in an uptrend.
The first type of scalping is referred to as "market making," whereby a scalper tries to capitalize on the spread by simultaneously posting a bid and an offer for a specific stock. Obviously, this strategy can succeed only on mostly immobile stocks that trade big volumes without any real price changes. This kind of scalping is immensely hard to do successfully, as a trader must compete with market makers for the shares on both bids and offers. Also, the profit is so small that any stock movement against the trader's position warrants a loss exceeding his or her original profit target.
In addition to knowledge of basic trading procedures, day traders need to keep up on the latest stock market news and events that affect stocks—the Fed's interest rate plans, the economic outlook, etc. So do your homework. Make a wish list of stocks you'd like to trade and keep yourself informed about the selected companies and general markets. Scan business news and visit reliable financial websites. 
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