With material design icons you just specify them with the prefix and icon name that you can find using the website. As an example, https://materialdesignicons.com/icon/weather-sunset would be used like:
icon: 'mdi:weather-sunset'
But what about other icon sources? I found this icon at a different icon site. How can I use this in Lovelace?
You can use the simpleicons set:
Why would I be interested in a brands icon set?
Why wouldn’t you?
Many integrations can be identified by their brands.
It’s your only other option unless you use a custom card that supports local png icons. And the only one of those I know of has been abandoned.
It is possible to take SVG based icons and code them up in a way that you can include them (as custom icons) with your Home Assistant…but its not so easy.
