Always double check citations created by a citation generator or manager. Automatically generated citations frequently have issues with proper formatting, and might also have spelling errors or missing information. Cover your bases and double check their work!
Zotero is a free citation manager available as a plugin in your web browser and a desktop app. Zotero collects and cites research from multiple types of sources, lets you save PDFs and notes, and helps you organize your research info folders and projects. Zotero has extensive documentation and tutorial videos to get you started.
Like Zotero, Mendeley is a free reference manager that allows you to manage citations, PDFs, and notes. It works as a web browser plugin and desktop app, and also has help guides available.
Zotero and Mendeley are comparable in a lot of ways, but you might find that you prefer one over the other. If you're on the fence about which one to use, see the link below for a comparison chart for the two managers.
EasyBib is a free resource that allows you to build citations within a browser that can then be copied and pasted. Supports MLA, APA, and Chicago.
BibMe is a free resource that allows you to build citations within a browser that can then be copied and pasted. Supports MLA, APA, AMA, and Chicago.
Citation Builder is a free resource from the NCSU Libraries that allows you to build citations within a browser that can then be copied and pasted. Supports MLA, APA, and Chicago.