Historians often rely on archives for research - places where original and unique documents of the past are preserved. The best source in the world for Gustavus college history is on the third floor of the library in the College and Church Archives. Here papers, photos, and artifacts are selected for their historical value and are preserved. Some of the collections have been digitized, but not all by a long shot. To use the archives, it's best to make an appointment or stop by and be prepared to wait as archives staff find what you need.
If another archives may have what you want, see if they have a website. Often, even if archival material hasn't been digitized, archivists may have created "finding aids" that list what's available. You might even be able to request that a particular document be scanned for you, depending on whether you can identify what you want and archives staff have time to help. (They are often run on a shoestring budget.)
There is no primary sources section in the library. Try searching for a topic and adding the word "sources" or "letters" or "personal narrative" or "diaries" or search for the name of a historical figure as an author. You also will find leads to primary sources within secondary sources. In addition, the library has several sets of facsimiles - reprinted books.
We also have historical runs of a number of popular magazines. These are shelved on the lower level alphabetically by title. There's a printed index to popular American magazines, The Reader's Guide, available in the Reference section to help you search by subject and year.
In addition to the image sources listed on the first tab of this guide, many projects and organizations make digitized materials available online. Here are some examples.