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.
If the indicator can establish a time when there's an improved chance that a trend has begun, you are tilting the odds in your favour. The indication that a trend might be forming is called a breakout. A breakout is when the price moves beyond the highest high or the lowest low for a specified number of days. For example, a 20-day breakout to the upside is when the price goes above the highest high of the last 20 days.
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.