Primary sources are documents or artifacts created at the time under study. Secondary sources might analyze or summarize historical events, but primary sources record history as it happens. There is no single, systematic way to locate primary sources, and you might have to get creative to find what you need. Depending on the period of time you are studying, a good primary source might be a newspaper or magazine article about a historical event, a diary or letter written by a historical figure, or a piece of media such as a painting or cartoon.
Newspapers and magazines make periodic records of historical events, and usually make some effort to distinguish fact from opinion, making them invaluable primary sources. Most newspapers do not make their archives available on the open web, however, the following collections of newspapers and magazines are available online:
There are many government and university projects that digitize and preserve books, manuscripts, and other archival documents. These repositories are all very large, containing millions of documents, and their contents are not always text-searchable.