What you get
The download is a zip containing favicon.ico (16, 32 and 48px in one file), favicon-16.png and favicon-32.png, apple-touch-icon.png (180px), icon-192.png and icon-512.png for progressive web apps, a site.webmanifest, and an icons.html with the markup. Drop the files into your site root and paste the HTML snippet into your <head>.
How it works
Your image is drawn onto a canvas at each required size, scaled to fit (its aspect ratio is kept and any extra space stays transparent), and exported as PNG. The .ico is assembled from the small PNGs — the modern format every current browser reads. A square source gives the cleanest result; very detailed logos lose legibility at 16px, so simpler marks work best as favicons.
Notes
SVG sources are rasterised at each size, so they stay crisp. The manifest's name and theme colour come from the fields above; adjust them and the snippet, manifest and download update without re-processing the image. Need to resize a single image instead? Use the Image Resizer.
Privacy
Everything — decoding, resizing, the .ico and the zip — happens in your browser. The image is never uploaded.