Drop an image onto the window, or click the frame in the center of the screen to choose one. Clicking the image puts a swirl at that spot. Drag the center dot to move it, and drag the ring to change how far it reaches.
Pick a swirl in the Swirl panel and its position, radius, angle, and falloff appear in the child panel beside it. A positive angle turns clockwise, a negative one turns the other way. The wheel zooms, and holding space while dragging moves the image. Save the result as a PNG at its original size from the Main panel.