Denied unemployment, how do I appeal? - any advice?

I got a denial letter last week saying I left my job voluntarily, but I was let go as a mechanic. I am in Cleveland, in case local advice matters. The letter lists a deadline and a hearing process, but it is hard to follow. If you have appealed before, what helped you prepare?

Legal aid offices and some workforce centres help with unemployment hearings at no cost. A call is worth it.