To determine where your Zotero data is being stored, go to the Advanced section of Zotero settings and look under Files and Folders. The default directory is listed under Data Directory Location. You are strongly advised to use the default location for your Zotero data.
Data syncing
All of the item information, notes, and attachments imported into your Zotero collection are stored in this directory on your computer in a file called zotero.sqlite. If you would like to be able to access your collections from any computer connected to the Internet, then you must register with Zotero for an account and sync your data between your computer and Zotero's server.
Everything in your collections, including notes, links, and tags, will be saved to the server. There is no limit to the amount of data that can be synced. (Note this is different from file syncing, which is covered below.)
After you have registered with Zotero, open Zotero's Sync settings and enter your Zotero account login information in the Data Syncing section.
At the next screen you will be provided with options for data syncing. If you choose Sync automatically, each time changes are made, Zotero will automatically sync your data. If you disable this option, you can sync manually at any time by clicking the Sync with zotero.org button (
) in the upper right corner of the Zotero application. Attached files are only indexed on the computer where they are added. Checking the Sync full-text content option syncs the index across computers, ensuring that the full text search includes all files, regardless of where they were indexed.
By default, Zotero will merge your local Zotero library with your library on zotero.org—any changes you make in one place will be applied to the other and on all other synced computers. If an item has changed in multiple places between syncs, you'll receive a conflict resolution dialog asking which version you'd like to keep. In the rare case that you want to completely overwrite your server library with the contents of your local library or vice versa, you can use the Sync Reset Options.
File syncing
While your data is included in the zotero.sqlite file, attachments like PDFs, EBUBs, web snapshots, etc. are located in a storage folder created when you installed Zotero. In the image above, the option for file syncing with Zotero is selected. Data syncing syncs library items, but doesn't sync attached files (PDFs, audio and video files, images, etc.). The options here allow you to set up file syncing to accompany data syncing, using Zotero File Storage. Each Zotero user is given 300 MB of free Zotero File Storage for attached files, with larger storage plans available for purchase.
File syncing with ZotMoov
If you use the ZotMoov plugin for Zotero, you can use any cloud service to keep your library synced across computers, such as Dropbox or Google Drive. See the ZotMoov tab for instructions.