Select the fill tool and press to open the settings.

Choose 'Gradient' from the 'Fill Style' menu.

Choose 'Circle' from the 'Gradient' menu.

When you are finished with these settings, press the 'Done' button.

Press and hold the spacebar or to begin drawing. Use which will begin drawing a line. The start of the line will be where the foreground color begins, the end of the line where the background colors begins. Release the spacebar or to apply the gradient.

Using a circle gradient.

Using an oval gradient.

Using a square gradient.

Using a rectangle gradient.

Using a line gradient.

Using a cylinder gradient.