If you have already downloaded your preferred broadcasting software (Fansly recommends OBS - Open Broadcaster Software), you will need to connect your software to the Fansly servers. To do that in OBS, navigate to Settings → Stream. Please select 'Custom' as your server, and input both your Stream Server and Stream key (both of which can be found here: https://fansly.com/creator/streaming).
If you’d like to stream from a mobile device, please download an app that supports RTMP ingest - this is the technology used by your app to connect to Fansly servers.