A primary source is a first-hand account or other evidence coming directly from an event. This might include letters, legal documents, speeches, diaries, interviews, data, and even video or audio recordings.
A secondary source is one that someone has created by engaging with the primary sources. Scholarly articles, nonfiction books, newspaper articles, and other interpretations are secondary sources.
Each situation will be different, but you may consider:
Below is a list of additional official websites that offer free access to online collections of primary resources.