Worksheets exist in the browser window only and are not stored on the server, by default. To save all your queries and results, use the Save button which is the middle graphic of the menu bar. It looks like this:
Depending on browser, desktop, and OS-settings, the "Ctrl+S" key combination may do the same thing.
Saved worksheets can be loaded or deleted using the FileOpen button which is the left-most button in the menu bar. It looks like this:
Depending on browser, desktop, and OS-settings, the "Ctrl+O" key combination may do the same thing.
A pop-up menu should appear with the list of saved worksheets with an option to either load or delete the worksheet.