Zotero is a free online citation manager which also has software versions for Windows, macOS and Linux. The usefulness of Zotero is enhanced by the Zotero browser plug-in that allows you to import citations of articles, books, and other resources from database search results into Zotero for storing and managing. Zotero is able to generate bibliographies of citations in a variety of formats (e.g., APA, MLA, IEEE, Chicago).
The first time you use Zotero, you will need to create an account. Your account will allow you to store citations indefinitely for repeated use.
After creating your account, go to the Zotero Download Page and install the Zotero Connector browser plug-in which will allow you to import citations from database results and web pages. Zotero Connector is available for Chrome, Firefox and Safari web browsers.
A bookmarklet is available that will work on most other browsers.
You may also download and install a standalone Zotero program for your laptop or desktop computer. Versions are available for Windows, MacOS, and Linux. Plugins are available for additional functionality of the standalone program, including word processor plugins to insert in-text citations, footnotes and bibliographies into Microsoft Word documents, Google Docs files and LibreOffice files.
After logging in to the Zotero Web version, you'll likely be brought to your list of citations. (If not, click on "My Library" at the top of the screen.) If you already have some citations saved to Zotero, they'll be listed on your screen which should look like the image below. Options include adding and tagging references, placing them in collections, and creating bibliographies.
Click image to enlarge ...