If your sessions are a panel of speakers, you can specify which one is the moderator. They display first in the session details. Moderators are a sub-category of speakers and will show under speakers in your directory. It’s not a role so there is no moderator directory and no option to add a person as a moderator in the form.
Choose a moderator from the session add/edit page, or add moderators in Column K of the schedule spreadsheet.