Unlike Siri or Google Now, Cortana, Windows 10's voice-response digital assistant, lets you control what it knows about you, so that it can pop up relevant reminders and display information of interest. You do this by making selections in Cortana's Notebook, in your Contacts, and in the Maps app. The last two let you tell Cortana which contact is your spouse, and which places on the map are your home and workplace. That way, Cortana can pop up a reminder to call a spouse, or let you know how long a commute will take based on traffic.
Like Google Now (and now Siri, to some extent) Cortana can listen for a key phrase, in this case 'Hey Cortana' will wake up to answer your requests. But before she can do any of this, you need to enable her the first time you click in the Windows 10 search box. This also involves granting permission to use your location, mic, contacts, email, messages, and browser history, though you can adjust these permissions to taste. Cortana can show you local news, sports, and weather info, and even tell you a joke or two.