If you're thinking of starting an appeal after a decision has been handed down by a trial court, you may think that you need to bring in some new evidence that will change the case. However, more often than not, this is not actually going to happen. Rather than operating like a trial, an appeal is typically about searching for errors in the first decision and the way that the law was applied in order to have the aforementioned decision overturned.
You're going to need to prepare what is known as a brief. This simply lays out your point of view and your argument, telling the court why you think that the lower court got the verdict wrong. This generally means that you believe that court made a mistake, and this is your chance to tell the appellate court what that error was.
With your new argument in mind, as stated in the brief, the court will then go back over the documents from the lower court. The goal here is not always to see new evidence or to hear new testimonies, but to determine if the lower court came to the wrong decision based on the evidence that it had on hand.
Therefore, the appellate court typically assumes that the trial court got the facts right, and it is just seeing if the judgement lines up with those facts. There are cases in which the findings of the jury do not fit with the evidence, and the appellate court will consider these if the facts really don't line up. However, the court doesn't use a new jury or attempt to establish many facts on its own.
The appeals process is complicated and technical. You must make sure that you understand the process and have experienced legal guidance before it begins.
Source: FindLaw, "Appealing a Court Decision or Judgment," accessed May. 22, 2015