Snowflake is available in Tor Browser stable for all platforms: Windows, macOS, GNU/Linux, and Android.
You can also use Snowflake with Onion Browser on iOS.
If you're running Tor Browser for desktop for the first time, you can click on 'Tor Network Settings' on the start-up screen and then select 'Use a bridge'.
Click on 'Select a built-in bridge' and choose 'snowflake' from the dropdown menu.
Once you've selected Snowflake, scroll up and click 'Connect' to save your settings.
From within the browser, you can click on the hamburger menu ("≡"), then go to 'Preferences' and go to 'Tor'.
Alternatively, you can also type
about:preferences#tor in the url bar. Check 'Use a bridge' and 'Select a built-in bridge'. Then select 'snowflake' from the dropdown menu.