rt pivots the turtle clockwise (rt stands for "right turn").
The turn is measured in degrees.
rt 90
Notice that the turtle will not actually move in the new direction
until you tell it to move forward with fd.
When using a pen, putting rt between two fd moves can draw an angle.
pen purple fd 100 rt 120 fd 100
Notice that the angle used by rt is the exterior angle.
The interior angle added to the exterior angle will be 180.
For example, the 60 degree interior angle drawn by the program
above corresponds to the 120 degree exterior angle swept out by
the turtle.
rt turns right from the turtle's point of view, so
if the turtle is facing downward, when it turns right from its
point of view, it will end up facing left from your point of
view. The demo below can be clicked a few times to show
different starting directions.
turnto random 360 pen orange fd 100 lt 100 fd 100
rt can also be used to draw curves by using a second argument.
Read the reference page on arcs.