Did you just try to call someone?
If you make a call and no one comes back to you to could be many things. That person just isn't around at the moment. Another possiblitiy is your signal is not being heard. For most any reasons it's suggested to just monitor the frequency for a while. Someone might come on, just to say they are "monitoring" as well, so you can talk to them and find out what you wanted to know.
Please don't be shy about staying on the frequency, especially to monitor. It's not like a telephone, either when you are talking with someone there's not a "timer" presssure to finish up, especailly if it's an interesting subject(s).
The longer you stay on 147.200 you will find out how things work better for you !