Zotero is a free reference management tool that allows you to conveniently save, edit and share references from a single library. It also allows you to centralise notes and annotations, as well as create and export citations and bibliographies.
Zotero can be downloaded here. The latest version, Zotero 6, comes with an in-built PDF viewer, allowing you to read PDFs in app and add notes and annotations that can be accessed from anywhere. A web version is also available, though this guide focuses mainly on the desktop version.
Click start in the bottom left of your desktop
Go to the Zotero download page
Without a Zotero account, all references will be saved locally to the device your are using at that time. With a free Zotero account, you can sync your library across devices, allowing access to your references from anywhere. This is recommended, especially if you use Zotero in the library and might be using many different computers!
Once you have set up a Zotero account, sync your library by:
Comprehensive documentation is available on the Zotero Website for more advanced issues
For other issues, consult the Zotero Forums