In forex, currencies are always traded in pairs, like EUR/USD. A pair shows how much of one currency you need to buy one unit of the other. Pairs are grouped into major, minor and exotic, depending on which currencies are in them.
The first currency is the base. The second is the quote. The price tells you how much of the quote currency you need to buy one unit of the base.
This means 1 euro costs 1.10 US dollars. If you buy the pair, you buy euros and sell dollars. If you sell the pair, you do the opposite.
These pairs all include the US dollar and another big currency. They are the most traded pairs in the world.
Minor pairs, also called cross pairs, do not include the US dollar. They are made from other big currencies.
An exotic pair has one major currency and one currency from a smaller or emerging economy.
This page is for learning only and is not financial advice. Forex trading can lead to quick and big losses, and you can lose all the money you put in. Trade with real money only after you understand the risks.