The HoloLens emulator allows you to test holographic apps on your PC without a physical HoloLens and comes with the HoloLens development toolset. The emulator uses a Hyper-V virtual machine. The human and environmental inputs that would usually be read by the sensors on the HoloLens are instead simulated using your keyboard, mouse, or Xbox controller. Apps don't need to be modified to run on the emulator and don't know that they aren't running on a real HoloLens.
The emulator may take a minute or more to boot when you first start it. We recommend that you keep the emulator open during your debugging session so you can quickly deploy apps to the running emulator.
Controlling the emulator is very similar to many common 3D video games. There are input options available using the keyboard, mouse, or Xbox controller. You control the emulator by directing the actions of a simulated user wearing a HoloLens. Your actions move that simulated user around and apps running in the emulator respond like they would on a real device.
When the emulator launches, you will see a window which displays the HoloLens OS.
To the right of the main window, you will find the emulator toolbar. The toolbar contains the following buttons:
The default tab within the Additional Tools pane is the Simulation tab.

The Simulation tab shows the current state of the simulated sensors used to drive the HoloLens OS within the emulator. Hovering over any value in the Simulation tab will provide a tooltip describing how to control that value.
The emulator simulates world input in the form of the spatial mapping mesh from simulated "rooms". This tab lets you pick which room to load instead of the default room.

Simulated rooms are useful for testing your app in multiple environments. Several rooms are shipped with the emulator and once you install the emulation, you will find them in %ProgramFiles(x86)%\Program Files (x86)\Microsoft XDE\10.0.11082.0\Plugins\Rooms. All of these rooms were captured in real environments using a HoloLens:
You can also record your own rooms to use in the emulator using the Simulation page of the Windows Device Portal on your HoloLens.
On the emulator, you will only see holograms that you render and you will not see the simulated room behind the holograms. This is in contrast to the real HoloLens where you see both blended together. If you want to see the simulated room in the HoloLens emulator, you will need to update your app to render the spatial mapping mesh in the scene.
The Account tab allows you to configure the emulator to sign-in with a Microsoft Account. This is useful for testing API's that require the user to be signed-in with an account. After checking the box on this page, subsequent launches of the emulator will ask you to sign-in, just like a user would the first time the HoloLens is started.