Choose the part for your button
Drag the circle over the part you want. Drag the pink dot to make it bigger or smaller, or click anywhere on the picture to move it there.
Or press Add pictures to pick them from your computer, or copy an image and paste it with Ctrl + V. Pictures saved on this computer always work; one dragged straight off a website sometimes can't be copied.
Any picture works — a photo, a screenshot, a whole sheet of drawings. Once it's here, press Choose area to pick the exact circle you want as the button.
Drag the circle over the part you want. Drag the pink dot to make it bigger or smaller, or click anywhere on the picture to move it there.