The Ellipse tool draws a round object on the image.
To draw an ellipse:
Click the button.
In the Tool Options, select the Line Width. Selecting Filled is optional.
Select two colors with the Color Picker. The primary color creates the border color and the secondary color fills the ellipse.
Select a Blend Mode.
Select an Opacity.
Hold the mouse button and drag the pointer across the image to draw the ellipse.