import turtle

def main():
    # Create a screen object in turtle
    screen = turtle.Screen()

    # Set screen dimensions
    screen.setup(width=300, height=300) 

    # Set background color
    screen.bgcolor("lightyellow") 

    # Create a turtle object
    pen = turtle.Turtle()
    pen.shape("turtle") # Change the turtle's shape
    pen.color("green") # Set the turtle's color
    pen.pensize(3) # Set the pen's size

    pen.forward(100) # Move forward by 100 units
    pen.right(90)
    pen.forward(100) # Move forward by 100 units
    pen.right(90)
    pen.forward(100) # Move forward by 100 units
    pen.right(90)
    pen.forward(100) # Move forward by 100 units

    screen.exitonclick()

if __name__ == "__main__":
    main()