Moving a Sheet into its own Book

1. With a multi-sheet workbook open, click and hold the tab of the spreadsheet you want to move and drag the cursor outside of the book into an empty space (i.e. not over another workbook).
2. The cursor will change to  to indicate when you can release it.

This will remove the sheet from the original book and create a separate spreadsheet.
You can save the file using the default name Book;2 or use File | Save As to give the spreadsheet a new name.