<aside> <img src="/icons/help-alternate_blue.svg" alt="/icons/help-alternate_blue.svg" width="40px" />
What?
<aside> <img src="/icons/help-alternate_yellow.svg" alt="/icons/help-alternate_yellow.svg" width="40px" />
Where?

Main interface

Citation level

Use citation mangers to keep track of all the reference work you come across. There are many free and paid options, but by far the most popular with academics are Zotero and **Mendeley.** You can read about others here.
Once you start collecting enough publications to actually develop expertise in your area and put together a useful literature review, you’re going to lose track of them, both in terms of remembering the content and literally losing track of the files. A reference manager minimally organizes the citations themselves, letting you group related work into collections, see bibliographic details, and tag/label citations. Most reference managers also allow you to store and/or access the files themselves from within the app.
When you finish your review and you need to produce the list of references, the manager will do that for you in the style of your choice. Easily swap between APA, MLA, Chicago, and many field- and publication-specific formatting options.
My preference is Zotero. Why?