How do authorize my new computer (windows 10) for iTunes?

Authorize your computer in iTunes - Apple Support

Thanks Amy, while the link takes you to support that addresses PC, it is probably the OS systems prior to W10. The control/B function gives no drop down in W10. FYI

Ctrl-B should enable/disable the menu bar in all supported editions of Windows. It certainly works fine on all three Win10 systems that I have iTunes deployed on. You can also make the menu bar temporarily available by tapping the ALT key, or by turn it on permanently by opening the "mini menu" (black/white icon at the top left of the iTunes screen) and selecting Show Menu Bar.

The same menu also gives access to authorization, using iTunes Store submenu: