MBP not mirroring on TV

[cherrytutu]

Just got my first MBP and am trying to hook it up to our 55" flatscreen.
I have the Dynex mini-display port to HDMI adaptor AND a rocketfish HDMI cable. When I go to the HDMI3 channel on our TV, all that shows up is the homepage on my MAC (the one that come on it and looks like space.

Not sure what I am doing wrong...
TIA

 

[GGJstudios]

How to: Connect a MacBook, MacBook Air, or MacBook Pro to a TV

 

[simsaladimbamba]

System Preferences > Displays >> Arrangement >>> Mirror Displays

But it will reduce the resolution of one device to the lowest resolution available.
For instance, if the TV has a resolution of 1366 x 768 and the MBP a resolution of 1440 x 900, the MBP's resolution will be now 1466 x 768.