Appellate law deals mainly with what judgments are appealable, how appeals are brought before the court, what will be required for a reversal of the lower court (e.g., a showing of "abuse of discretion," "clear error," etc.), and what procedures each party must follow.
Appellate law also involves such issues as posting and challenging appellate bonds, writs of habeas corpus (Habeas Corpus Act), writs of execution, writs of restitution, writs of quo warranto, writs of procedendo, writs of supersedas, writs of prohibition, writs of mandate, writs of administrative mandamus, writs of certiorari, and other forms of discretionary relief, pursuit of further relief on remand, post-verdict motions, and other issues.