Appeal deadline questions after an unemployment denial - 16 weeks in

I got a denial letter last week saying I left my job voluntarily, but I was let go as a retail manager. I have read a lot of threads here and could not find my exact situation. The letter lists a deadline and a hearing process, but it is hard to follow. If you have appealed before, what helped you prepare?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.