In a polar point (r, θ), there are two parts. These are the radius r and the angle in radian.
In the given question, our radius is 1, and our angle is -pi/3 in radian or -180/3 = -60 in degrees.
To plot this, we need to consider first the angle. Since we have -60 degrees here, we have to move clockwise and the point is located in the 4th quadrant. Somewhere in the black line below. (360 - 60 = 300 degrees)
After that, we have to consider the radius that is 1.
The above graph shows where the point (1, -pi/3) is located)