Cortana is a digital personal assistant similar to Siri or Google Now. The first article discusses how to turn Cortana on and Cortana's various setting options, the second article gives examples of what to ask Cortana and the third article provides more information about Cortana. The video demonstrates Cortana in action. Cortana can be used with any device (PC, tablet or phone) that is running Windows 10.
To view David Neild's article go to I Installed Windows 10 and Now I'm Talking to My Computer.
To view another article by David Neild, go to 18 useful Voice Commands to Try with Cortana.
To view Microsoft's information on Cortana, go to What is Cortana?