Zotero File Storage is a cloud-based syncing and storage solution for PDFs, images, web snapshots, and any other files attached to your Zotero libraries. Zotero File Storage synchronizes the files in your personal Zotero library to all your computers, allows you to share the files in your group libraries, and makes files available through the zotero.org website, all for free.

Want to purchase more space? Answer this first: Are you an institution or is this for personal storage?
Institution
Personal

Visit the storage FAQ. For more in depth information on how storage functions, see Zotero's documentation.