Generally speaking, being long in a certain currency pair (such as USD/EUR) means betting on the rise of USD/EUR; Shorting is the opposite. Its principle can be said to come from the promotion of funds. When the total amount of multi-dollar funds is greater than the euro, it can relatively promote the rise of the dollar/euro, which is like the increase of people's demand for dollars, which is the same as buying anything else. The more people buy, the higher the price. On the contrary, more people sell dollars and buy euros, and the euro will rise.

In the final analysis, foreign exchange trading is buying and selling between different currency pairs to obtain the currency difference.