Windows 10: Showing pictures on TV with HDMI cord

What you do depends on what mode your in, Extend, or Duplicate etc. You press the Windows logo key + P to select what mode you want. You may also have to go to Settings > System > Display and rearrange the displays to match your physical locations. Then just open your image and drag it to the display you want to view it on.

If your running multiple displays you have the option to extend your desktop to the second display. Each screen is independent of the other. I'm running dual screens on my laptop as I type this. I'm using Extend and have outlook open on my external display, and IE open on my main laptop display. The first time I launch an app or program it opens by default on my main display. I can then drag it over to my secondary display if I want to. After that it remembers what screen it was last opened on. In duplicate, both screens show the same thing, the second display just mirrors the first one. It was the same deal in Windows 7. nothing has changed as far as I know?
Sometimes Windows will show the second display as being on the left, when its really on the right. When that happens your cursor will hit what seems to be a wall when trying to go from one monitor to the other. In Settings > System > Display the detected screens will have numbers. Click Identify to see if the displayed placement matches your physical layout. If they don't match drag one monitor across so they match.