How do I disable Cortana?
Settings->Cortana & Search Settings
You can't absolutely, positively disable Cortana because there is a process named Cortana that is part of the OS and integral to doing Windows Search. You can, though, disable Cortana as an electronic personal assistant (and/or remove anything she already knows about you in the cloud) and having her include web results as part of her searches (which uses Bing to get them).
I am still awaiting clarification from Microsoft as to whether they recognize a difference between the Cortana process, which one really can't get rid of, and the Cortana Service [which is what I think of as "full Cortana personal electronic assistant" functions]. One should be able to avoid using the Cortana Service if one so chooses, but it doesn't look like the Cortana process is optional in any way.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story