I need to know where the tension er pulley is located on a 19997 Chevrolet Cavalier

Follow the belt, it will be the one that is NOT power steering, alternator, Water pump or harmonic balancer. Their should be a 1/2" square hole to apply tension once bracket is loosened.
Flashlight may help.
Some photos:
http://www.theautopartsshop.com/Search/Default.aspx?Pat=1997+Chevrolet+Cavalier+Belt-Tensioner-Assembly&Key=Year+Auto+Car-USA+Parts&gcode=ChevroletCavalier1997FS458908920&gpartnum=97CheCavalier%2FFS45890

http://www.ehow.com/how_6101366_install-belt-1997-chevy-cavalier.html
Drivers side, under alternator is Tensioner according to 2nd link.

It looks like, based on Stratmando's link, you'll need to use a socket and breaker bar on the idler pulley bolt. A regular ratchet wrench may not provide the leverage you will need.