This video is really good to watch if you are studying about American Revolution.
"The Shot Heard Round the World" is a phrase that represent several historical incidents. It's meaning is that the American Revolution made the world changed. The colonies united and fought against the Great Britain, which everyone knew that Britain had the most powerful military, while the colonies had minute men. When the Americans won the war, other colonies from other parts of Europe decided to follow American's step-to make their own revolution.
Click this link for The American Revolution Timeline: http://www.timetoast.com/timelines/the-american-revolution-timeline--24