Cortana is the name of the interactive personal assistant built into Windows 10. You can give her instructions, and talk with her by using your voice or by typing.
Here's a short video, to show you the kinds of things Cortana can do to help you.
Cortana's many talents
If you press Windows key + S on your keyboard, you will open Cortana. Then click on the question mark to see a list of examples of what she can do.
As you can see, there are already many things that Cortana can help you with. When inside the application you can click on these listed items and see an example of typical commands you might say for each one.
Setting up Cortana
You can quickly setup Cortana and help her to get to know you. In the Notebook section you can go through the different categories and choose any options which relate to you.
Also in the Cortana Settings tab you can see the 'Other privacy settings' link.
This gives you the options to choose, adjust or delete what Windows and Cortana learn about you.
How to use Cortana in Windows 10
To search with Cortana in Windows 10, you can simply type the keyboard shortcut Windows + S. Then you can type in the search field, or click on the microphone icon and say a command.
Windows + S - Search (including Cortana)
To activate Cortana in listening mode only (like I did in most of the video), you can use the keyboard shortcut Windows + Shift + C. Then you can say a command or question while she is listening. (You will need a microphone.)
Windows + Shift + C - Cortana (Talk to her)
If you prefer to call Cortana without using the keyboard or mouse, go into the Cortana settings and choose 'Let Cortana respond to "Hey Cortana."'. Then when you want to use Cortana, just say "Hey Cortana."
Help improve Cortana
Be sure to post feedback to Microsoft of the kinds of things you would like Cortana to be able to do, by using the Provide feedback tab.
Cortana's development is evolving quite quickly. What are some of your favourite commands for Cortana?