A red eared slider is semiaquatic. Those types of turtles like a temperature between 75 to 78 degrees fahrenheit (23 to 25 celsius). I suppose you have water for it to swim in. If you dont then get it, if you do, then make sure it's not too cold for it. Having a cold water makes it sick, so it wont eat.
I'm not realy sure about the red eared's diet, but I think you could try guppies, mostly goldfish. So you could drop about 15 to 20 feeder guppies (preferably goldfish), that's one of the slider's best meal.
And get a veteran to help, dont just take our words for it.