WOW!!!! Lets ALL go buy a ridiculously overbred turtle species, throw caution to the wind, put it in a cardboard box until someone on the internet tells us what kind it is or what to feed it. If you people have ever visited this site before you should know not to ask stupid questions like "I just got this cute baby turtle, what does it eat?" You know every one will harp on you for not doing your research first.
Have you ever heard or a petstore? Hows about a freakin’ Wal Mart they sell Aquatic turtle food ie.. red eared slider food ( or Reptomin floating food pellets) They should also be offered little bits of lettuce(Romaine not Iceburg) Also try mealworms or even little brine shrimp if you can find them. Variety is key. Put it in an aquarium. The rule of thumb for tank size is 10 gallons for every inch of carapace (top shell) length. Place somthing in the tank fot it to climb on to and completely dry out (basking area). Place a basking lite over the basking area. Most people would reccomend using a UVB lite ,but recent studies (according to an article in reptiles magazine) indicate that UVB is not essentilal for juvenile turtle shell growth. This is debatable. But I wouldnt spend $75.00 on a lite bulb for a $5.00 turtle.
At the pet store you can find a "Turtle filter" the work very well and coct about thirty bucks. Even with the turtle filter you will still need to replace the water and scrub the tank at least once every two weeks. turtles especially RES are very dirty. So I have covered feeding, lighting, and filtration. That should pretty much do it. Enjoy your cute little turtle!!!!!!!!!!!!!!!!!!!!!