Ad 1. Turn off ads on the Start menu. Microsoft calls them “suggestions,” not ads, and they appear sporadically at the top of the app list on the Start menu. To do so, click Start > Settings > Personalization, then on the left choose Start. Slide the entry “Occasionally show suggestions in Start” to Off.
Ad 2. Turn off ads in File Explorer. I haven’t seen any ads there lately, but the hooks are all in, and you’d be well advised to clobber them now. Microsoft calls them “sync provider notifications,” and supposedly they serve a legitimate purpose, notifying you of the status of your data sync with cloud providers. In practice, at least so far, it’s just an advertising hook. To turn off the ads, start File Explorer, click View, then Options, then on the View tab, uncheck the box marked “Show sync provider notifications.”
Ad 3. Turn off ads on the lock screen. Microsoft calls it “Windows Spotlight,” and it serves no known purpose other than to get you to click on some clickbait such as “Like what you see?” To throttle these ads, click Start > Settings > Personalization. On the left, choose “Lock screen.” In the Background box, choose anything other than Windows Spotlight.
There are other ads in the Notification (“Action”) center — Start > Settings > System. Choose “Notifications & actions” on the left, then pick and choose. And there are ads on the Windows Ink workspace, if you use it. Click Start > Settings > Devices, then on the left choose “Pen & Windows Ink” and slide Off “Show recommended app suggestions.” There are also ads in the Share dialog, but if you use the Share dialog you’re too far gone anyway.
And of course, the advertising icons on the Start screen drive many people nuts. Just right-click on anything you find offensive (Candy Crush Soda Saga, anybody?) and choose Uninstall.