The wiki page uses incorrect location of Menubar options, perhaps from older versions of LibreOffice, to describe "Freezing Rows or Columns as Headers". "View" rather than "Window" Menu option is used. https://help.libreoffice.org/Calc/Freezing_Rows_or_Columns_as_Headers
It's worth noting that the offline documentation, included with my installation of LibreOffice 5.0 on RHEL7, shows the correct location of the relevant Menu option.
Created attachment 134306 [details] screenshot-libreoffice-calc-help
In 5.1 or 5.2 these options were moved to the View menu from the Window menu. The online help by default reflects the help content of the latest version - 5.3 currently and 5.4 soon-ish. This page is correct, it documents the 5.3 UI. The older versions can be viewed on these links: https://help.libreoffice.org/5.0/Calc/Freezing_Rows_or_Columns_as_Headers - this shows the entries in the Window menu. https://help.libreoffice.org/5.3/Calc/Freezing_Rows_or_Columns_as_Headers - this shows the entries in the View menu.