Denied unemployment, how do I appeal? - first time posting

My claim was denied after 13 weeks of waiting, and the letter says I have a short window to appeal. Any experience at all would help. I have not done a hearing before and I am nervous. If you have appealed before, what helped you prepare?

Thanks for writing this out. I went through something close to it 14 months ago, and it settled down once I kept a simple log of every call and form.

I printed my emails in order and wrote a one-page timeline. The hearing officer kept going back to it.