Yes, your turtle is usually considered a hatchling at that size considering that they can be anywhere from .8" to 1.25" when hatched. The only difference in caring for hatchlings that I can think of now is the temperature and feeding. Hatchlings need a water temperature of a constant 78 degrees and a basking temp at least ten degrees higher or around 88-90 degrees. Turtles older than a year need a water temp between 72-75 degrees. Also turtles under a year old should be fed daily, once-a-day the amount of pellets that would fit inside their head if it were hollow. Closer to a year old and over, they are fed every other day (the same amount). Also, veggies should be introduced as soon as your RES is settled into his new habitat. The younger they are the easier it usually is to get them eating the veggies that they need for a balanced diet.
As far as caring and setting up his home, read through the main site and the stickys here on the forum. There's a lot of info to learn on caring for turtles so if you have specific questions after reading, just ask.
Start here:
Basic Care and here:
Care Sheets
