Imagine a trader who expects interest rates to rise in the U.S. compared to Australia while the exchange rate between the two currencies (AUD/USD) is 0.71 (it takes $0.71 USD to buy $1.00 AUD). The trader believes higher interest rates in the U.S. will increase demand for USD, and therefore the AUD/USD exchange rate will fall because it will require fewer, stronger USD to buy an AUD.
Most retail investors should spend time investigating a forex dealer to find out whether it is regulated in the U.S. or the U.K. (dealers in the U.S. and U.K. have more oversight) or in a country with lax rules and oversight. It is also a good idea to find out what kind of account protections are available in case of a market crisis, or if a dealer becomes insolvent.
This is the only way you can really stay on top of your trading. Allow yourself to make mistakes - and don't make the mistake of being scared to prove yourself wrong - you'll be in a much better position for it in the long run. You have to be comfortable with accepting that mistakes are inevitable, especially in the early stages. It's all part of the learning curve.
The 2nd method is by performing a carry trade, where you can profit by buying a currency with a higher interest rate, and selling a currency with a lower interest rate. An example of this would be the USD/CHF (Swiss franc). If you buy USD/CHF, you are buying the USD, and their interest rates are higher than Swiss interest rates, so if you hold the position overnight, every day you hold the trade you will make money, and the money will be deposited in your brokerage account.
More specifically, the spot market is where currencies are bought and sold according to the current price. That price, determined by supply and demand, is a reflection of many things, including current interest rates, economic performance, sentiment towards ongoing political situations (both locally and internationally), as well as the perception of the future performance of one currency against another. When a deal is finalized, this is known as a "spot deal." It is a bilateral transaction by which one party delivers an agreed-upon currency amount to the counter party and receives a specified amount of another currency at the agreed-upon exchange rate value. After a position is closed, the settlement is in cash. Although the spot market is commonly known as one that deals with transactions in the present (rather than the future), these trades actually take two days for settlement.