Cortana is Microsoft's version of a personal virtual assistant.
As such, it is just Clippy with a voice. As Cortana responds to voice commands, the room has to absolutely quiet. Any question must be asked in English as spoken by a Swede eating a triple decker sandwich and must be asked using the vocal equivalent of an interrobang. Naturally, since Cortana only uses answers that can be found on Bing, chances are you're not going to get an answer anyway.
If you order something to go from a restaurant or use Cortana to make reservations, you will be guaranteed to get a callback to see if that was really you that called or a prank call made by your kids or parrot.
Of course, you will forget that Cortana is never turned off so it will record all your arguments, sleep talking ans sex noises to be cataloged for the amusement of Microsoft employees and use in porn videos.