Enter a filename pattern using {w} as the width placeholder (e.g. image-{w}.jpg), list your target widths, set the sizes attribute and alt text. The img and picture markup update live for you to copy.
The {w} token in your filename pattern is replaced by each width you list. For example image-{w}.jpg with widths 320 and 640 produces image-320.jpg and image-640.jpg in the srcset.
The img version uses one srcset with width descriptors so the browser picks a size. The picture version adds <source> elements offering a modern format (AVIF or WebP) with a fallback for browsers that don't support it.
sizes tells the browser how wide the image will render at different breakpoints, e.g. (max-width: 600px) 100vw, 600px. The browser uses it with srcset to choose the most appropriate file before layout.