After you click any export button in Silverbucket, that export file will be created in the background. Once the file is ready, you can download it from the 'My Exports' view.
This sketch cannot currently be displayed in exports
You can enter 'My Exports' view by clicking the notification link 'View in My Exports' when the creation is finished - or you can navigate there manually at any time through your account's icon located top-right in Silverbucket:
This sketch cannot currently be displayed in exports
In there, you can download or delete any file you have created in the past 7 days: