Providing the username and password of your zotero.org forum account here allows you to sync Zotero libraries across multiple computers. This can be set to occur automatically, but can also be done manually by pressing the sync button in the main Zotero pane.

See Syncing for more information.

See File Syncing for more information. When you use Zotero File Storage, you can view your current usage and quota in your Storage Settings.