Importing things into Zotero
Alright, so I've got this great little app that lets me annotate papers. How do I put papers in it?
Using the Zotero Connector
This is maybe the easiest way of putting papers into Zotero. There's a Zotero web browser extension called Zotero Connector. When I see a paper I want to read while searching online, I click on the Zotero Connector extension and it automatically saves it to my library. This can be linked to a hotkey to make it even slicker.
The Zotero Connector web browser extension appearing in a drop-down menu.
Using the document's DOI/ISBN
If the website the paper is on can't be read by the Zotero Connector extension, a nice possible alternative is to use the paper's DOI or ISBN if it has one. In the Zotero desktop app, you can add papers using either of these identifiers by clicking on the wand icon.
A dialogue box appears below the wand icon, prompting for an ISBN, DOI, or other identifier.
Using Zotero Save
This one I only learned about recently. If you don't have access to the desktop app or your usual browser, you can always go to Zotero.org/save, which lets you save items via both the Zotero Connector-style and the ISBN/DOI method.
The Zotero.org/save website, prompting for a URL, ISBN, DOI, or other identifier.
Manually
If all else fails, you can use the desktop app to manually add papers. It's a little tedious, but it will work in every circumstance!