What is a "legal brief?" What is its purpose? Who prepares it in a criminal case?

What all components ( or necessary ingredients ) need to be included for an effective Legal Brief?

After a legal brief has been filed with the Court, describe/explain how the case then proceeds and oral arguments are conducted in criminal appeals.

Research how an appeal hearing is conducted? Differentiate it from a trial process. Basically, what are the differences between a trial court ( original jurisdiction court) and an appellate court ( appellate jurisdiction)?

Locate a current event criminal case that was reversed on appeal. Cite the case, summarize the facts, and discuss on what legal basis it was reversed.