Zotero
In your time at Harvard, you'll hear more than one librarian suggest that you use Zotero, a "citation management tool." Zotero will be great for big projects that require you to keep track of many sources -- semester-long research assignments, capstone projects that are research heavy, and senior theses, for example.
Next semester, or next year, you might want to graduate into using Zotero itself. It will take the process of collecting and organizing sources and incorporating footnotes or in-text citations to the next level.
A good guide to Zotero itself, if you're interested, is available here: https://guides.library.harvard.edu/zotero