Got a denial letter for unemployment, what now?

My claim was denied after 18 weeks of waiting, and the letter says I have a short window to appeal. This is my first time dealing with any of this. My employer's version of events does not match mine, and I have emails that show it. Did you bring documents or only talk?

File the appeal before the deadline, even if you are unsure. You can gather documents afterwards. That is the one part I would not wait on.