Never capture a wild turtle and never release your pet turtle to the wild. If you can no longer keep your pet turtle get in contact with a turtle rescue. If you have purchased your turtle from a local pet store ask them for assistance in finding your pet a new home.
http://www.petloverscompanion.com/ListingList.aspx?cat=181&subcat=0
http://www.petturtle.com/resources.htm

In your turtles environment do not use tap water or city water. You can capture rain water use bottled water or add an ingredient to remove chlorine from the water. This can be purchased from most pet stores. Whatever you choose to do the water needs to be kept clean.
Do not over feed your turtles. Feed them a little at a time. I feed my guys Reptomin pellets, tadpoles, grated carrots, hibiscus flowers and leaves and on occasion fresh brine shrimp. I hand feed my turtles but be careful they can attach to your finger.
Read about your particular breed of turtle. http://www.austinsturtlepage.com/Care/caresheet-red_ear_slider.htm

After you become familiar with your pet you will notice his personality emerging and how he interacts with others. Check his eyes and his shell for problems. Turtles can become stresses look for those signs. Enjoy your pet for many years.