Currency carry trade refers to the act of borrowing one currency that has a low interest rate in order to purchase another with a higher interest rate. A large difference in rates can be highly profitable for the trader, especially if high leverage is used. However, with all levered investments this is a double edged sword, and large exchange rate price fluctuations can suddenly swing trades into huge losses.
In developed nations, state control of foreign exchange trading ended in 1973 when complete floating and relatively free market conditions of modern times began.[48] Other sources claim that the first time a currency pair was traded by U.S. retail customers was during 1982, with additional currency pairs becoming available by the next year.[49][50]
Despite being able to trade 24 hours a day, 5 days a week, you shouldn’t (Forex trading is not quite 24.7). You should only trade a forex pair when it’s active, and when you’ve got enough volume. Trading forex at weekends will see small volume. Take GBP/USD for example, there are specific hours where you have enough volatility to create profits that are likely to negate the bid price spread and commission costs.

Balance of trade levels and trends: The trade flow between countries illustrates the demand for goods and services, which in turn indicates demand for a country's currency to conduct trade. Surpluses and deficits in trade of goods and services reflect the competitiveness of a nation's economy. For example, trade deficits may have a negative impact on a nation's currency.
Forex (FX) is the marketplace where various national currencies are traded. The forex market is the largest, most liquid market in the world, with trillions of dollars changing hands every day. There is no centralized location, rather the forex market is an electronic network of banks, brokers, institutions, and individual traders (mostly trading through brokers or banks).

The broker basically resets the positions and provides either a credit or debit for the interest rate differential between the two currencies in the pairs being held. The trade carries on and the trader doesn't need to deliver or settle the transaction. When the trade is closed the trader realizes their profit or loss based on their original transaction price and the price they closed the trade at. The rollover credits or debits could either add to this gain or detract from it.

Inflation levels and trends: Typically a currency will lose value if there is a high level of inflation in the country or if inflation levels are perceived to be rising. This is because inflation erodes purchasing power, thus demand, for that particular currency. However, a currency may sometimes strengthen when inflation rises because of expectations that the central bank will raise short-term interest rates to combat rising inflation.
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.