Every platform hides it somewhere slightly different, and several of them hand out a key that only works once. Pick yours below for the exact steps, the server address, and the mistake that catches most people.
Two pieces of information tell a platform where your video should appear: a server URL, which is the same for everyone on that platform, and a stream key, which is yours alone. Anyone holding your key can broadcast to your channel, so treat it like a password. If you ever paste one somewhere public, reset it on the platform straight away.
Beamd streams pre-recorded video to these platforms around the clock, with your computer switched off. For YouTube you can skip the key entirely and connect your account instead. For everything else, paste the server URL and key once and it is remembered, encrypted.