Primary Sources are original materials or firsthand accounts of historical events. Some examples could include diaries, newspaper articles, and letters originating from the time you are studying.
A helpful resource on differentiating between primary and secondary sources can be found in this University of Massachusetts Boston LibGuide.
Fordham University hosts the Internet Medieval Sourcebook, which is an online collection of primary source texts.
There are two ways to search in this resource:
1. Use the search box in the top right corner to carry out a keyword search; or
2. Browse through the Selected Sources, Full text Sources, or Saints' Lives pages (I have found using Ctrl + F to search for instances of keywords on the page can be helpful while browsing).
Please note that this resource is freely available online, and therefore the editions and translations of these primary texts that have been collected are generally older (since they must be in the public domain, and no longer under copyright). However, you could consider searching either in Quick Find or MMSO to track down a newer edition.
In Quick Find, the Library of Congress Subject Headings (LCSH) for a given work are listed in the bottom half of the item record next to Subjects.
Subject headings that end in --Sources, --Correspondence, --Personal narratives, and similar are generally assigned to materials that include primary source materials.
Click on the subject heading to view all records that have been assigned to it.