Turtles in super flat will wander around aimlessly, but will attempt to stay near water. They will hide inside their shell if any creature larger than them gets too close. When hiding in their shell, they are resistant to nearly any type of attack. You can flip a turtle onto its back by right-clicking it. The poor creatures are completely vulnerable while on their back, and will take a while to roll over again. right clicking a turtle with a pickaxe hides its name and health bar and a medallion will change its name .Turtles are unique in the fact that they drop man-made objects when they are killed.
They drop chests in Yogbox.
To tame a turtle, drop (Q by default) sugarcane or melon nearby. Once tamed, turtles can be named, will follow the player, and grow slowly over time. Right clicking a tame turtle with anything but a pickaxe or Medallion will put it on your head. If a turtle is injured and you have sugarcane, put it onto your head and right click it with sugarcane in your hands. It will eat the sugarcane and will regain its health. If you have a turtle on your head and you're on a horse, like bunnies, the horse will go a lot faster. If you have a turtle on your head and you go through an opening 2 bricks high, the turtle will die.
They are most likely to spawn in a swamp, or near sugarcane. You can increase their spawning numbers in the options.