First choose the color you want for the shell, then roll it into a ball. Next you have to shape it into a half sphere. What I do is press the ball against my table to get a flat side. Then I just shape it with my fingers. Now it should look like a shell.
Next using the color of clay you want for the skin, roll four tiny ovals for the legs (they don't have to be perfect ovals, just make sure they're all about the same size). These are going to be a lot smaller then the shell, about 1/10 of the size is good, but you can go smaller if you want.
Take one of the ovals you just rolled out and press it against the bottom of the shell. Keep on pressing until you've flattened the bottom of the leg and it is firmly attached. Continue this with the other three legs. Make sure you space them evenly and leave enough room for the head and tail.
It should look like this...
Now roll out a tiny sliver of clay, it should be about 1/5 the size of the legs. This is going to be the tail.
In between two of the turtle's legs, attach the tail like so.
Here's what the back of the turtle should look like.
Next roll out some clay for the head. This should be about 3x the size of a leg. Roll it out into a teardrop shape.
Now using black clay (or whatever color you want to use for the eyes) roll out two 2-mm balls of clay. Then carefully attach these to the head, make sure they are evenly spaced.
Now you can attach the head to the body! Be careful not to squish anything else while attaching it!
Now you're done making your turtle! All you need to do is bake it according to the instructions on your brand of clay :)
You can even give your turtles neat shell designs if you want. After you make the shell just add on a design like swirls, polka dots or whatever you want. You could even paint the shell after your turtle is baked.