A primary source is an original document (or item). In other words, it was created during the time you're studying.
If I were studying the U.S.'s independence from Britain, then the Constitution of the United States of America would be a primary source.
A secondary source is something that was created after the fact and refers directly to a primary source.
They might give more background information, but they can also carry bias.
If I wrote a book about the U.S. Civil War, then a love letter from Private John Doe to his fiance would be a primary source, while my book would be a secondary source.
Where do I find sources?
Libraries are excellent repositories of sources and information! Librarians are trained professionals and are happy to assist.
At a library you can generally find:
Museums & Archives
Museums and archives are especially good for finding primary resources. Like librarians, museum curators and archivists are trained professionals.
At museums and archives you can generally find:
In addition, many museums are supported by a historical society which likely has additional useful information. Archives are good sources for geneological information.
There are a lot of useful sources online. You do need to be careful that the ones you find and use are credible, and not everything online is for free, but the Internet is a fantastic resource where you can find:
and much, much more.
Remember that a librarian can help you find what you're looking for on the Internet!