Primary sources are produced at the time of the event or phenomenon you are investigating, and they purport to document it. They reflect what someone observed or believed about an event at the time it occurred or soon afterwards. These sources provide raw material that you will analyze and interpret. Primary sources can be published or unpublished (archival).
In general, published primary source material covers a wide range of publications, including first-person accounts, memoirs, diaries, letters, newspapers, statistical reports, government documents, court records, reports of associations, organizations and institutions, treatises and polemical writings, chronicles, saints' lives, charters, legal codes, maps, graphic material (e.g. photographs, posters, advertising images, paintings, prints, and illustrations), literary works and motion pictures. Some of these materials were not published at the time of their creation (e.g. letters), but have subsequently been published in a book.
Obviously there are different types of primary sources for different historical periods. Church documents and saints' lives serve as primary sources for the study of medieval history, while newspapers, government reports, and photographs serve as primary sources for the modern period. Moreover, what constitutes a primary source depends in part on how you have formulated your research topic. In other words, there is no intrinsic or distinguishing feature of a text that makes it a primary, rather than a secondary, source. Many sources, whether visual or textual, can serve as either primary or secondary sources. The key is how you use the material. In order to determine whether a source might be primary or secondary for your purposes, you must consider it in relation to your particular topic.
"Rerum Novarum": An historic text; it enunciated the late 19th-century Roman Catholic position on social justice, especially in relation to the problems created by the Industrial Revolution, and it emphasized the Church’s right to make pronouncements on social issues as they related to moral questions.
You can find published primary sources by using the online catalog and published bibliographies. You can also look at secondary literature on your topic to ascertain what sources other scholars have used in their research. Remember that there is nothing in the online catalog record for a book that indicates whether it is a primary or secondary source, since this is not necessarily an inherent or essential characteristic.
If you're having trouble finding primary sources, then go back to your secondary literature: what sources have other scholars consulted? These should be cited in the endnotes and/or described in an essay in the back of the book.