There's not a whole lot to know.  It's a TV.  It's just like every TV you've ever had, just a WHOLE LOT more powerful.
1)  RTFM, this is very important and will answer most of your questions
2)  As a high quality TV, how you connect your source will be important - there are currently 6+ common ways to connect your TV to a video source.  Google around for these or RTFM.
3)  The power of your TV is with HD.  You can get HD programming a number of ways - over the air (think rabbit ears or antenna), cable or satellite or depending on your area via your telco.
4)  Calibration - not necessary for most TV owners, absolutely necessary to get the quality you paid for.  They're accustomed to putting a TV on the shelf and be done with it.  However, if you want to get the most from your new TV a calibration disc will do wonders.  A professional calibration is the very last 15% of getting the most from your new TV...while nice not many people will benefit from it unless they are really into video and know what to look for.