I’ve never been in a large event. What is the etiquette?

You are in for a treat.  Event etiquette is to stay to the right of the course to allow passing on the left.  As you approach someone from behind a polite call of, “On your left.” This let’s them know you are passing them on their left.

We will have a variety of paces participating in the event.  If you stay to your right on the course it will leave space for faster participants to pass on the left.