Style Sheet assigns the specified style sheet to the current notebook.
A check appears beside the style sheet currently assigned to the notebook.
Mathematica standard style notebooks are kept in SystemFiles/FrontEnd/StyleSheets. Style notebooks created by users can be put in Configuration/FrontEnd/StyleSheets. Any style notebooks in these directories will automatically be listed in the Style Sheets submenu.
The Other command opens a dialog box to find style sheets not listed in the Style Sheet submenu.
The commands in this submenu set the option StyleDefinitions on the selected notebook.