Occasionally i will connect my Macbook to the tv with the Thunderbolt port adapter and a HDMI cable. I ran into this problem the other day when i was using my connections on a new tv, It was only showing my Macbook wallpaper background on the tv. After looking around in the display settings i fixed the issue.
Fixing Macbook to tv showing wallpaper background only
Go into System preferences -> Displays If connected right you will see an Arrangements tab click on this. In the Arrangements tab there will be two boxes or monitors side by side, a menu bar will be on one of them. Drag this menu bar across to the other ‘monitor’ image. This makes the second monitor, the tv your main screen. to have both the tv and Macbook display the Macbook screen as normal, check the Mirror display option in the bottom left.