Scalping in forex is a common term used to describe the process of taking small profits on a frequent basis. This is achieved by opening and closing multiple positions throughout the day. This can be done manually or via an algorithm which uses predefined guidelines as to when/where to enter and exit positions. The most liquid forex pairs are preferred as spreads are generally tighter, making the short-term nature of the strategy fitting.
When trading forex, you always speculate on whether the price of the base currency will rise or fall against the counter currency. So in AUD/USD if you think AUD will rise against USD, you go long (buy) the currency pair. Alternatively, if you think AUD will fall against USD (or that USD will rise against AUD), you go short (sell) the currency pair.
Locating the trend: Markets trend and consolidate, and this process repeats in cycles. The first principle of this style is to find the long drawn out moves within the forex markets. One way to identify forex trends is by studying 180 periods worth of forex data. Identifying the swing highs and lows will be the next step. By referencing this price data on the current charts, you will be able to identify the market direction.