Mirror Displays does what it says, it mirrors your internal MBP display onto the external, you see the same content on the TV as you see on the MBP's internal display. As the internal display has a maximum resolution of 1440 x 900, the image on the external display is 1440 x 900 too, unless the external TV does not support a resolution that high.
If you uncheck/disable the Mirror Displays option, you extend your MBP's display. So you can have 1440 x 900 on the internal display and 1920 x 1080 on the external TV, if it does support it (have a look at the manual or the product page in the www).
You don't see the same content on both displays, as it is not mirrored but extended.
So if your TV supports 1902 x 1080, don't use the Mirror Displays option.
The Arrangement tab lets you position your displays, if you have unchecked/disabled Mirror Displays.
The one with the white bar on top is the one display with the Menu Bar, normally your MBP.
The other blue box (
not a time machine of course) is the external display. You can drag it wherever you want.
If the TV is on the left side of your MBP, drag it to the left, to avoid confusion.
If it is on the left, drag the blue box to the left, if it is on the top, drag it to the top.
You can also drag the white bar (Menu bar) to the external TV, so you can have the Menu bar on the external TV, but using a TV as a computer display is not advised due to its low resolution and pixel depth.
You can edit your post via the
, which is left of the
button, which itself is also left of the
(multi-quote) button, as consecutive posts by one user are not welcome.
It looks like this on the bottom right of every of your posts:
