I have participated in panels and have “headed” them. Moderating is a little different.
1. The moderator should not have “a dog in this fight”. If he has an opinion about the subject matter, the audience should not be able to tell. Folks are attending to hear the panelists, not the moderator. This can be hard.
2. The moderator has to politely keep the discussion from wandering off topic.
3. And insure that each panel member gets to speak on all topics with roughly equal time. Some folks can say a lot in a few words, others can ramble on for hours and say nothing. Everyone should at least have the same opportunity. You have to be brave and cut folks off sometime to hear from someone else.