To stream to Facebook, you will first need to setup your stream on Facebook.
To do this, click on Live Video
On the next page, you can select Use Stream Key in the Get Started tab.
Once selected, copy and paste both the Server URL (Stream URL in Riverside) and the Stream Key into the Facebook slot in Riverside.
On the stream page in Facebook, you can also toggle the settings to use persistent stream keys, select latency settings, etc.
Once all information is entered into Riverside, make sure the toggle is enabled. The stream will now initiate once the recording button has been selected in your studio.