Primary sources are original documents, artifacts and other records. They are the evidence closest to an event that helps us understand what was happening at that time.
Secondary sources are the stories people who weren't there tell about those events--articles, books, and other documents that interpret, summarize, or critique.
To help you remember, think of a target made of concentric circles.
In the center is the historical event or topic you are studying.
Moving outward, the first ring is where you'd find primary (original) sources. This is as close as you can get to actually being there. Primary sources are firsthand accounts created by eyewitnesses, like diaries. They may also preserve data about an event, like a birth or death certificate.
In the second ring, then, are the stories told by people not present at the event. The historian is the second (or third, fourth, or more!) person to tell the story, and so a book written by a historian is a secondhand or secondary source. In some cases the lines between primary and secondary sources begin to blur. Watch the video below to find out more.