Forex trading is the buying and selling of currencies from different countries, essentially trading the currencies against each other.
Individual traders or retail investors engage in this trade by means of speculating the future rates of various currency pairs. As such, these traders will buy or sell any currency pairs, whose rates are likely to go up or down, respectively, according to market forecasts.
It is important to note that as a retail trader, you cannot engage directly in the trading, but through facilitation by a forex broker.