The Zotero Connector allows you to save article PDFs, web pages, and video files with one click of a button. You will need to install the Connector on your browser of choice.
You can review the Zotero Quick Start Guide for the basics on setting up and using Zotero.
Zotero comes with basic citation styles, however, there are many others that you can add, including AMA, individual journals, etc. Zotero provides documentation for installing additional styles using the Zotero Style Repository or downloaded CSL styles.
For specific questions and more documentation, you can review the Zotero Knowledge Base.
Saving an article citation and PDF with one click using Chrome extension at top right
Zotero's desktop library with customizable folders, article information, and any attached PDF or file
Zotero's web library (limited free storage)
If you need to quickly generate a citation without downloading any software or saving a file, you can use ZoteroBib.