Primary sources are documents or other artefacts that were created at the time an historical event occurred. They are the "raw material" used by historians to study the events of the past.
Some examples of primary sources include diaries and letters, photographs, news articles, advertisements, speeches, government and legal records, radio broadcasts and films from the period under study to name a few.
Think of who might have collected the type of primary source you are looking for, then search that specific website e.g. historic British government documents? Search the British National Archives website.
Limit Google searches to web addresses that are likely to collect the sources you need by adding site:___ to your search terms. For example, the search war posters site:gc.ca will search the Canadian government websites for war poster collections.
Assess carefully the sources you find. You should be able to easily determine who made the source available, and when and where the source was originally published or created. Look for sources being offered by credible organizations like libraries, universities, museums, or other organizations with expertise in the field.
Visit the American Library Association for more advice on evaluating primary sources.