Explain Items List
When first starting the standalone version, one goes to File > New Item and sees the list of all the available items (item types?). However, where does one find an explanation of what they each are?
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My first use of the program takes me to File, then New Item, which seems to be the correct way to start doing something. But as i mentioned, without an explanation for these items, how does one choose which to select?
https://www.zotero.org/support/getting_stuff_into_your_library
Otherwise, like @adamsmith says, the categories are flexible. Use Journal Article for academic journals, Magazine Article for non-academic magazines, Book Sections for chapters, Report for documents issued by companies or agencies, etc. We can be a lot more helpful if you tell us what sort of item you are having trouble classifying and we can recommend an appropriate type for it.
If one takes that standard approach, then one is faced with the confusing list as I mentioned.
And for the most part that's working -- we get a lot of questions here, but your confusion about File --> New Item is very, very rare.
I'm sorry this was confusing to you and if you have specific questions left I'm happy to help, but I'm not interested in a general discussion about this.
Examples:
Author Menu: "Zotero lets you specify editors and translators, too. You can turn an author into an editor or translator by selecting from this menu."
Quick Format Citation Dialog: "Type a title or author to search for a reference. After you've made your selection, click the bubble or press Ctrl-↓ to add page numbers, prefixes, or suffixes. You can also include a page number along with your search terms to add it directly. You can edit citations directly in the word processor document.
Save Button: "Click this button to save any web page to your Zotero library. On some pages, Zotero will be able to save full details, including author and date."
The most useful and most common method for that sort of thing in today's computer programming is a mouse cursor hover-over pop-up.
Also, I noticed that the center pane displays "Zotero Quick Start Guide", but when one expands it down it only says "Welcome to Zotero". There is no guide. Do you happen to know anything about that?
I even noticed that the Firefox add-on that was promised with the stand-alone install, never happened. Obviously, the whole instructions thing leaves a lot to be desired.
Anyway https://www.zotero.org/start shows up when you first install Zotero. What was promised? Are you referring to Zotero 5.0 which is in beta at the moment and will provide (as you can read in the changelog):
A Unified Zotero Experience
The two full versions of Zotero, Zotero for Firefox and Zotero Standalone have been replaced by a single standalone application for users of all browsers. A new Zotero Connector for Firefox, similar to the extensions available for Chrome and Safari, allows you to save to the Zotero desktop application or zotero.org in a single click.
If you're a current Zotero for Firefox user, you'll be automatically upgraded to the Zotero Connector for Firefox, and you should install the Zotero application if you don't have it already.
Blog post forthcoming with additional details
See also this post.
By the way, how does a connector differ from an addon or plugin?
Why didn't the standalone simply say to install both? In fact, if one's browser is not supported, it would be better to know that first by being directed to install the addon first. Doesn't that make sense?