Please note that the "Windowing" operator is part of the "Series" extension which you need to install as well: https://marketplace.rapidminer.com/UpdateServer/faces/product_details.xhtml?productId=rmx_series
You can also go into the menu "Extensions" in RapidMiner, click on "Marketplace (Updates and Extensions)..." and type in "Series" in the search box. Follow the steps to install the extension.
After you installed the extension (and restarted), the "Windowing" operator will be part of your RapidMiner installation.
Hope this helps,