A style describes is the layout and formatting of the output from Zotero.

Zotero uses the open standard CSL (Citation Style Language) for configuring citation formatting. CSL is independent of any particular application, document format, or programming language. More details can be found here

Well, that depends what you need to output!

If you are writing for a specific journal, it may be already supported in the Zotero Style Repository. If not, you can request a new syle.

If you are writing a report or assignment, then your teacher or university might specify a format. If not, chose the style of a journal or professional association in your field.

These pages should answer most common questions about Zotero Styles:

If your question is not answered above, try these steps to getting help,

Search through Zotero's forums

Or post your question at the Zotero Styles Forum..