The first time you use the GoToWebinar system, you may have difficulties. After doing it once, you will find it easier. You do need a good, stable internet connection, first of all.
If your internet connection does not seem to be the issue, you can troubleshoot your system by using the help pages provided by the Go To Webinar system
Also, here is a short, quick start video by Go To Webinar that will help you understand the system for future calls:
GETTING STARTED ON GOTOWEBINAR