Capitalism is an economic system and an ideology based on private ownership of the means of production and their operation for profit.
Mercantilism was a type of national economic policy designed to maximize the trade of a nation and especially to maximize the accumulation of gold and silver.
So in other words,. Mercantilism is a type of economic system based on international trade. Merchants export goods to other nations and import goods to their own nation in hope of making a profit. Because many businesses in a modern capitalist economy do the exact same thing, mercantilism can be interpreted as an early form of capitalism.