What you're looking for is a VGA to Composite adapter (something like this). If your graphic card does not have a VGA output, you'll also need a DVI to VGA adapter which should have been included with your card. (something like this). This will bring the video output of your graphics card to your TV.
You'll also need a 3.5mm stereo to RCA Audio cable (something like this) to connect the audio from your computer's sound card to the TV.
you need to connect HDMI (from the computer) to audio video (3 RCA plugs) on the TV.
you need an adapter, yes there is such a thing http/www.amazon.com /s/?ie=UTF8&keywords=hdmi+ to+rca+converter& tag=googhydr-20& index=electronics&hvadid=4657488197&ref=pd_sl_1afui5yww2_b
take spaces out of above link
anyhow there's all kinds of adapters available, and you need to check and see what type of output is on your computer...HDMI? DVI? and then order the appropriate adapter for RCA composite video / audio
some graphics cards have a special plug, and an included adaptor for the special plug.
this adapter will have:
check to see if your graphics card came with the special plug.
once you get the TV connected to the graphics card, you go into the graphics card software and it will allow you to adjust the resolution IF the TV says its okay.
the graphics card and television will 'handshake' and the TV reports what resolution adjustments are available.
there will be a difference is resolution between your monitor and your tv, however, you can use the tv for video as you have suggested by setting the television up as monitor #2 under display properties and having your desktop extend to this monitor (without the start bar). anything you want to play on said monitor just drag over to the tv (display#2) and fullscreen it. not the most ideal solution but it will work.