What size should my source image be?

At least 512×512 and square. Everything is downscaled from it, and detail that is not in the source cannot appear in the output. A simple mark works far better than a detailed logo: at 16×16 you have 256 pixels to work with.

Do I still need a .ico file?

Only for old Internet Explorer. Every current browser reads a PNG favicon, and an SVG favicon scales perfectly and is a fraction of the size. Shipping a .ico as well costs nothing and rules out one class of support question.

Where do the files go?

In your site's root or public directory, then paste the generated link tags into your HTML head. The tool gives you the exact markup with the right sizes and rel attributes.

Favicon Generator

Upload one square image and get every favicon size a browser or device asks for — 16×16, 32×32, 180×180 for Apple touch, and the 192/512 PNGs a web manifest wants — plus the HTML to paste into your head. All resizing happens in your browser.

Runs in your browser — nothing is uploaded

Questions

What size should my source image be?: At least 512×512 and square. Everything is downscaled from it, and detail that is not in the source cannot appear in the output. A simple mark works far better than a detailed logo: at 16×16 you have 256 pixels to work with.
Do I still need a .ico file?: Only for old Internet Explorer. Every current browser reads a PNG favicon, and an SVG favicon scales perfectly and is a fraction of the size. Shipping a .ico as well costs nothing and rules out one class of support question.
Where do the files go?: In your site's root or public directory, then paste the generated link tags into your HTML head. The tool gives you the exact markup with the right sizes and rel attributes.