Zotero's open source-ness has created a pretty rich ecosystem of applications and tools that work with it. Here are a few, and you can find more on the Zotero Plug-ins page.
I'll be adding more to this - I'm trying to make a series of shortish (around 20 minutes) screencasts that demonstrate Zotero.
Jason Puckett’s Zotero page (Georgia State) https://research.library.gsu.edu/zotero (Jason has also written a book, updated in a 2nd edition, Zotero: A Guide for Librarians, Researchers and Educators)
Getting Started and Installing Zotero (University of Michigan) https://guides.lib.umich.edu/c.php?g=282995&p=1885561
Migrating from EndNote to Zotero (Zotero.org) https://www.zotero.org/support/kb/importing_records_from_endnote
Migrating from Mendeley to Zotero (Zotero.org) https://forums.zotero.org/discussion/63737/moving-library-from-mendeley-to-zotero
Using Zotero with LaTeX/BibTeX (MIT) : Programmable Search Engine (google.com)
As a open source tool, Zotero has a robust number of third-party add-ons (plug-ins) that really make it even more useful. You can find a (not comprehensive?) list on Zotero's Documentation Page.
I have started some demo videos for these below.
Here are some additional videos (some I created, some from Zotero's documentation, that may be of use.
12/22/17: This was created as an aid for two webinars I did for WSU's Global Campus. (Links below). It was before Zotero's big 5.x update, so this will be slightly out of date, although mostly still usable.
Zotero Part 1: Getting Things into Zotero:
Zotero Part 2: Getting Things Out of Zotero (and into your research papers!)
[this one was not that good :-( I was really tired and it shows, especially when I was showing how Zotero works with Microsoft Word. I'll probably do an update and post it here.]