First, welcome to the forum.
My suggestion is to read through as much of the forum as you can (there's so much information contained here to help) and read the main site as well. The downloadable caresheets from the main site will help you get started with all the basic info that you need. After doing some more specific research just ask if you have any questions. Here's a few tips to get you started:
1) Recommended tank size is ten gallons per inch of shell (with multiple turtles add the shell lengths together)
2) RES love to swim even young ones so don't be afraid to fill the tank up leaving enough space where they can't escape.
3) Be sure to invest in a good filter (rated 2-3x's the size of your tank)
4) Both a UVB light and a heat light are necessary over the basking area to insure yourrr turtles stay healthy.
5) Accurate temps of water (78 for hatchlings, 72-75 for older turtles) and basking area (88-90) is extremely important to the health of your turtles. Along with a heater for the water invest in a couple of thermometers to read the temps of both the water and the basking area.
There's so much more to learn in caring for RES, but I'll stop there for now.
Just let us know how we can help you.