Forex is a worldwide market. It works 24 hours a day, 5 days a week. That means it is always open, except for weekends and national holidays when banks in various countries are closed. There are 4 geographic regions after which trading sessions are named: Pacific, Asian, European, and American. Sessions start at different times, which ensures the continuity of trading — when trading in one region is ending, in another region it is only preparing to open. The start and end of trading sessions vary by region. To eliminate confusion, trading hours are in Greenwich Mean Time (UTC/GMT).
On average, markets are open for 9 hours. There are quiet periods when low volatility is observed — it is best not to open positions then. Sessions also overlap, and these periods are considered the most volatile and therefore bring the most profit. The most active trading happens during the American trading session, while the Asian session is considered calm. Fluctuations can be observed at the open of the trading session and one hour before close.