You have a few ways to stop sharing your screen:
If you’re using cables, unplug them from your device.
If you’re connected wirelessly with Miracast, go to your device and end the connection. If you’re using a device running Windows 8 or later, press Windows logo key + K on your keyboard and select Disconnect.
Close the Connect app. If you don’t see the Connect app, select Task view at the bottom of the display, and then select the Connect app.
If you’re done working on the Surface Hub, select End session to end your meeting and the connection. The Surface Hub will be cleaned up for the next session, so be sure to save or send any files you want to keep.
For info on how to share the screen with people on a Skype call, see Present the screen during a call.