You have to do another window of the same workbook (Window>New
Window), and then do a Window>Arrange, check the check box for
"Windows of active workbook" and choose one of the display options
(Tiled, Horizontal, Vertical, Cascade). From either window, you can
go to different sheets so you have the ability to see two different
locations on the same screen.
When you are done, go to the window you want to close and then press
Ctrl+W to close it.