It's quite simple. You're responsible for helping put on one of the largest Subaru enthusiast festivals that ever happened, a one day celebration of the best car community in existence. In order for it to better and grow the community, the event has to be executed well. That's where you come in. While we have a few part time staffers (all formerly volunteers), volunteers such as yourself are the ones really running the show.
That all being said, by signing up as a volunteer, you're committing to arriving by your designated shift and working the whole thing! You'd be surprised how many people sign up and bail, leaving the event day a total struggle for the rest of the volunteers. Volunteering is work, but overall pretty easy, be it flinging event shirts to fellow attendees or scanning tickets. If you need relief or are miserable, it's up to you to speak up to a staff member.