To get a satellite connection, it is important to understand that because satellites move swiftly relative to where you are, it is important to use the best connection you can obtain. Ideally, the sky and horizon will be clear. You might be unable to connect to a satellite if you are under heavy foliage or in a dense urban environment (and the service does not work at all when underground).
To test the service, open Settings > Apps > Messages, then tap Satellite Connection Demo. This will guide you through the steps you must take to access these services.
You can also test the system from within the Emergency SOS or Messages apps. To try the first, open Settings > Emergency SOS; otherwise, open Settings > Apps > Messages and tap Satellite Connection Demo. It is a good idea to run the test so you develop a better understanding of how the system works before you actually have an emergency.