At least read over the basic care part of the main site. They have good start up info, including this section
http://www.redearslider.com/startup.html that provides you a list of everything you need and how to get it cheap.
the general feeding rule is to get a good brand of pellet, like Mazuri or Reptomin, and for a hatchling feed only the amount that would fit into your turtle's head if it were hollow every day. If it's an adult turtle, (over a year or around 4'' in length) a head sized amount every other day and feed greens and veggies everyday. Offering more than this can result in pyramiding which can damage your turtles internal organs. Don't be afraid to introduce veggies to your turtle as a hatchling, it'll make the conversion much quicker. Treats like shrimp and fish and stuff that's high in protein should only be offered no more than once every 2.5-3 weeks. Once a month would be preferable if you have to provide them at all.
Try and follow the 10 gallons per inch of shell rule. Get the largest tank you can manage now. Don't wait for your turtle to get big.
Provide a proper basking area where your turtle can dry off fully. And provide adequate lighting which consists of UVA (heat, that can come from an ordinary house bulb) and UVB (requires a special UVB bulb, they come in tubes or in compact bulbs). Make sure and place both lights over the basking area at appropriate levels.
Get at least two thermometers, one for basking, one for water. If your tank is larger than 40 gallons, I would recommend two thermometers for the water. I have three in the water in my tank (125 gallons).
DO NOT GET MORE THAN ONE TURTLE!!!
If you want multiple turtles, wait until you have at least a years worth of experience with this one. That will allow you time to experience all of the common problems associated with having one AND/OR more turtles. It will also give you time to actually read through the caresheet, which should not be negated due to advise offered here. Lots of things are being left out as we can't possibly cover it all in one post without copying and pasting directly from the main site.
DO NOT put gravel in your tank. This is a major health hazard. It can cause impaction and death in your turtle WHEN it is ingested. There is a sticky about this that you can look over.
Read the care sheet. I can't say it enough. It has tons of info there and it's formatted wonderfully, so it isn't daunting to read. Things like mating, you can skip over for now because you don't require it. But read it!
