Use Save As New Sheet to save a subsection of one sheet as a new sheet.
Often, in the Gigasheet workflow, users have hidden certain columns and filtered down to a certain row set, creating a view that's a slice of the total data set. Either because they want to do follow-on analysis on just the sliced result set, or perhaps for distribution purposes, they want to save off this view as a separate sheet.
To do this, choose File -> Save As
You'll be given the option to name the sheet, and choose which folder in your library it should go.
The new sheet will be created in your library, and can now be opened, analyzed, and shared like any other sheet.