So you might have obtained a Sony Xperia T and have heard you can connect it to a HD display, but are wondering how you do it.
Simply put you need the following adapter: http://www.clove.co.uk/samsung-official-mhl-adaptor-eia1uhunbecstd
At the time of writing Sony have not released their own adapter and this one from Samsung will allow you to connect your Xperia T to a HD screen.
Connect the adapter to a power supply, connect a HDMI cable from the HD display to the adapter and then connect the microUSB connection on the adapter to the Sony Xperia T.
Be aware that you need the adapter that works with the Samsung Galaxy S II an Samsung Galaxy Note. The adapter for the Galaxy S III and Note II does not work with the Xperia T.