First. welcome to the forum. Second, congratulations on your new turt. Third, thanks for being responsible and checking on the forum for proper care.
The main website has most of the basic info on what you need for a habitat.
http://www.redearslider.com/index_habitat.htmlYou're going to want an aquarium heater for the water.
viewtopic.php?f=9&t=31234For the basking area (the land area you've created with rocks), you'll need heat, UVA and UVB. The cheapest way to do that is two bulbs in clamp lights. The clamp lights you can get in the reptile section of any petstore, OR you can get the generic silver ones from the hardware store for considerably less. A regular incandescent light bulb will produce uva and heat. You'll need a special UVB bulb from the reptile section of the petstore for the UVB. The easiest is one of those CFL (twisty style) bulbs that is labeled UVB 5.0. Shine both lights at the basking area for about 8 hours a day.
viewtopic.php?f=6&t=10You'll need a thermometer. You want the water temperature to be about 76-78 and the basking temperature (adjust the height of the bulb) to be about 88-90.
You'll need really good filtration. This is probably the single biggest expense for keeping an aquatic turtle. Do NOT go by the ratings for filter sizes printed on the packaging. That's for fish... your turtle will produce a LOT more waste than fish. Follow this guide or ask on this forum if you have filtration questions...
viewtopic.php?f=9&t=30145Also, if your turtle has been neglected by the previous owner, post a few pictures on this forum of top / bottom / front / back. A quick visual inspection may help you identify any "issues" that need to be addressed from previous neglect. As always, nothing beats a visit to a qualified herp vet to assess the turtle's heath.