First of all, you will need the URL of the RTMP server and the correct Stream Key (it is sometimes called Stream ID) to define a streaming output. If the RTMP server is yours you’ll create these yourself. If the server belongs to a service provider, create an account and follow the instructions on their website on how to obtain these identifiers.
Create your account and obtain the RTMP URL and Stream ID as described on the website you are going to stream through.
Make sure that you have a second "Out" output, that will go to the stream in your compound: