What procedures are followed by an appellate court?
Federal appellate courts follow the Federal Rules of Appellate Procedure which is the rules and practices by which appellate courts review trial court judgments. State appellate courts follow their own state rules of appellate procedure. Appeals are usually limited to “final judgments” in both state and federal jurisdictions. There are exceptions to the "final judgment rule," including instances of plain or fundamental error by the trial court, questions of subject-matter jurisdiction of the trial court, or constitutional questions.
In considering an appeal, the court looks only at the official “record” of the proceedings in the lower court. New evidence is not considered most of the time. This “record” consists of the court reporter’s transcripts (everything said in court whether by the judge, attorneys or witnesses), and anything else admitted into evidence such as documents or objects, often called trial exhibits.
Written briefs filed by both sides of the appeal are also considered. For example, an appellant challenging a conviction or sentence files an opening brief, arguing how and why the conviction or sentence was legally wrong. A civil appellant will file a brief that persuades the appellate court that the trial court made an error that warrants a new trial or a modification or reversal of the lower court’s decision. In turn, the other party, (government in criminal cases) files its own brief to illustrate why the conviction, sentence, or decision should be upheld. The appellant typically has an opportunity to file a second brief in response to the respondent's position, and the appellate court may hear oral arguments from each side before reaching a decision on the appeal.