How does a conference call with 20 people work?

I am about to get on a conference call with 20 people, and I'm really scared because I don't know any of them. What am I supposed to do when I call in, say hi and interrupt conversation? How does one person take control of this entire conference call?How does a conference call with 20 people work?
Everyone will have a designated phone number to call into, with an access code #. There will be a 'leader' to introduce him or herself, then explain what the call is about. The leader may or may not tell people to introduce themselves. That can take a few minutes with 20 people so they might not. They will enable a 'mute' so there aren't people interrupting and being distracted with kids/dogs/pets, etc. The call is scheduled for a certain amount of time, usually an hour.