Denied unemployment, how do I appeal?

I got a denial letter last week saying I left my job voluntarily, but I was let go as a data-entry clerk. This is my first time dealing with any of this. 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.