I think I may have first heard and/or seen the word Mercantilism in my 9th grade US History class. If I remember correctly, I was only able to remember that it had something to do with money because "mercant" sounds like "merchant" and of course, merchants deal in trade. Any "ism" can be intimidating to study or learn, but this one really isn't that bad.
Do you remember the Stamp Act or the Intolerable (Coercive) Acts? Mercantilism is the name for the economic policy that those acts, along with the others not named, are grouped in. The idea behind Mercantilism was to get every possible penny from the colonies (North American, Indian, African, and Caribbean) to enrich the British Crown and expand the empire. The irony is that Mercantilism was its own undoing.
There were two documents that were written during the 18th century that played a role in the downfall of Mercantilism, at least from the North American colonies perspective...the Declaration of Independence and The Wealth of Nations by Adam Smith. Along with the notion that the colonists didn't like being taxed without representation in British Parliament was the fact that the British government prohibited imports to the colonies from foreign countries. What this did was limit the overall market for goods to be purchased as well as it drove up the price of imported British goods due to tariffs. Adam Smith, a Scottish economist, points out that Mercantilism was shortsighted and ineffective. To better understand the shortsightedness and ineffectiveness of the British policy, I suggest that you read, or attempt to read, his book. I just may add it to my list to read.
Source of information: The Intellectual Devotional: American History by Kidder and Oppenheim, pg. 18