Firstly you have to decide on the housing of the turtle, a 20 gallon tank is the best one as the turtle grows in a rapid speed and needs plenty of space to swim in. When you have bought inches the tank make sure you pour the water in to at least 7 inches giving the turtle space to flip over, also make sure you have a selection of smooth rocks as the turtle can not be under the water at all times and needs somewhere to bask.
One thing that has to always be your main priority is keeping the tank clean and i would highly recommend buying a canister filter as turtles produce copious amounts of waste! It is also important is drained and replaced with fresh water daily.

Heating and lighting is a huge part of a turtles life, temperature has to be between 70-80 degrees at all time. If the temperature is to low then the turtle may not eat when it goes into hibernation. This is easily achieved as all you need to do is install a heat lamp and UV light. The expose to the light makes sure the turtle does not get bone disease.

When feeding your turtle go for variety like insects, worms and raw fish this type of food is easy for the turtle to eat and will not decompose in water.

I hope the advice has helped and good luck with your new turtle!