Just a simple way to connect an Xbox One to a Xbox 360. I personally like to play Fallout or Skyrim while I'm waiting on a new match to start.
For this to work you will need...
2 HDMI cords (One came with the xbox)
And of course the consoles
Step 1: THE MOST COMPLICATED THING EVER (not Really)
Look at the component cord for the 360. It should have a little plastic nub that when plugged in covers the HDMI port. That plastic nub has no function and is made of hollow plastic. We are going to need to saw this off. Carefully saw the nub off it doesn't take much.
Step 2: CORDS
Now the easy parts. Plug in the first HDMI cord into the port on the Xbox One that is labeled for cable. Take the other end and put it into the newly opened HDMI port n the 360. The second cord goes into the port on the one labeled for tv yes the other end of this cord does go to your tv.
Step 3: TESTING
Turn on both of your Xboxes and say "XBOX GO TO TV". After a few seconds (sometimes a bit longer) it should play through your TV. If it says that the TV signal was lost or something of that nature use the HDMI cord that came with your Xbox One to link them together. That usually works. Sometimes you might have to jiggle the cord a bit. (DON"T TELL MICROSOFT THE SUPPORT TEAM FREAK OUT)