Currencies rise and fall against each other depending on various economic and geopolitical news. If you can buy low and sell high, you can make a profit in forex trading.
The Major Currency Pairs are the four most heavily traded currency pairs in the forex market. Because of the massive liquidity, you can always trade them with the lowest spread.
PIP
You might have noticed the forex quote has four places to the right of the decimal. The smallest price change that a given exchange rate can make is the pip.