In Forex, as mentioned, currency pairs are traded, the trading price of a given currency pair reflects the economic conditions of a given country versus the country of the other currency that makes up the pair.
One of the advantages of Forex is that its practice is accessible to everyone, because it is not necessary to have a high amount of money to perform operations. Starting as a "Mini trader", with an account of up to 50 dollars, you can start trading without any problems.
The most common currencies traded on Forex are: USD (US Dollar), EUR (Euro), JPY (Japanese Yen), GBP (British Pound), CHF (Swiss Franc), among others.
What sets Forex apart is that you can trade in both uptrends and downtrends. If you think a currency will rise in price, you can buy it. If you think its price will fall, you can sell it. Also, because Forex is so large, finding buyers and sellers is much easier than in other markets subject to liquidity.