I'd guess that you're using the Chrome or Safari connector but have Zotero Standalone closed, in which case the connector saves to the server. (This could also happen if Zotero shows as offline from the connector for some reason.) You'd then have to sync to get the items back into your local library for citing.

Make sure you have Standalone open and that it shows as online from the connector (if you hover over the toolbar icon in Safari or if you go the connector's options in the Chrome extension preferences),

I'm using Firefox; Zotero standalone is open.

Zotero version is 4.0.12; Zotero Word for Mac Integration is 3.5.7.

How do I find out if I have two databases...?

Also, I just restarted (again!), but the item I had just added is still not showing up on the list of available resources to cite once I've made a place for it in the document.

I've logged into the stand alone, so I'm in my library there. I can also go up to the Firefox menu bar and under Tools I can click on Zotero, which opens a different window--that window does not reflect changes I've made in the library (eg, some deletions, some additions, some changes to collections contents).

(I've been using the standalone library--I'd just as soon get rid of the other one, to avoid confusion. Though this doesn't affect the situation I have w/ unciteable items.)

Yes, Zotero Standalone had been installed, but you're right, I hadn't been using it. I've now opened it from my Applications folder and imported all the everything from the other one; I also restarted Word.

I was feeling very hopeful, but the item I'd added still shows up in my library and in the collection, and I still can't cite it.

hmm- somehow you seem to be rather confused about Zotero. To be quite honest I have a hard time even following your questions. So the easiest would be if you're around an academic library that supports Zotero or if you have a friend or colleague who knows Zotero decently well to ask for in-person help. This is much easier in person.

I can try to clear this up a bit, but this will take a while to disentangle.

Let's start with this:
There is absolutely no functionality in Zotero that requires you to log in.

There are three ways you can be looking at your Zotero library:
1. In Zotero standalone (ZSA), a standalone application accessible from your applications folder

2. In Zotero for Firefox (ZFF). A Firefox add-on that you can access by clicking on the "Zotero" logo at the bottom right of your Firefox browser. In a normal set-up this will require Standalone to be closed.

3. Online on zotero.org by clicking on My Library

You only need to log in for 3., but there is absolutely no reason to use it on a computer where you have 1. or 2. installed.

1. and 2. provide you with pretty much equivalent - and complete functionality. You can just edit item information for any item in the right hand panel.
They're also the only components that interface with the Word plugin. There is no way to have the online library interact with your word processor.

If you add data at to 3. it will only show up in 1. and 2. (and thus your Word plugin) after you sync:

So that's the basic structure.
I'm not even sure how and where you've been adding items, so that would be the first thing to clear up.

Re: logging in: having received your note, I clicked on the link to respond--this was not an option, without logging in

sure, you need to log in to use the forum. Just not to use Zotero itself.

You mention ZFF should require that ZFA be closed--it doesn't. I wonder if some of the problem is I'm using a Mac and that's not a platform you guys use very much?

at least one, if not both of the main developers use Mac principally, so that's certainly not the issue. I would recommend for the time being to make sure that ZSA is closed and only use ZFF, that will make things easier for you. Once you're done with your paper we can revisit this, but that's just complicating things right now and there's no particular reason to use ZSA if you're using Firefox anyway.

Next question is - how exactly are you adding items to Zotero?
That might help us understand where your Zotero items are going.

Finally, with which one, and how, do I edit an entry that's already been made?

You click on an item in the middle panel and edit it in the right-hand panel.

OK, so far so good.

Now add a new item using the url bar icon, check that it is in ZFF and then see if you can cite it in Word.
For files that you drag to Zotero, you first need to attach them to a Zotero item, else you won't be able to cite them. You can do so either by using right-click-->retrieve metadata for PDF or using right-click --> Create Parent Item

Control-click is right-click on a Mac (or two-finger click on a trackpad, depending on settings).

If right-click isn't available on your Mac (you should be able to configure "secondary click" on your Trackpad, though, e.g. as two finger tab or a right-click ), ctrl+click is the same as right click.

So you need to be able to distinguish between files and Zotero items.
Files in Zotero typically have a file-icon (you can easily recognize the PDF icon, e.g.), whereas Zotero items have the same type of icons you see in the URL bar - the blue book for books, the lined page for articles etc. Zotero items have many fields to add metadata in the right hand panel. Files just give you a couple of fields like Filename, Accessed, Modified that you can't directly edit.
Zotero items you can cite. Files you need to attach to a Zotero item before you can cite them.
Right clicking on a file will open a context menu that includes the option "Create Parent Item" towards the bottom.

If you create a new item using the green plus sign, then select an item type and manually enter the information you're good. Those are ready to cite. If you drag a file to Zotero from Finder or your Desktop, you need to follow the steps to attach it to a Zotero Item.

You can do this at any time.

glad that worked out.