which type of opinion becomes law in supreme court decisions
Judicial opinion A majority opinion in countries which use the common law system becomes part of the body of case law. Such decisions can usually be cited as precedent by later courts. In some courts, such as the Supreme Court of the United States, the majority opinion may be broken down into numbered or lettered sections. This allows judges who write an opinion "concurring in part" or "dissenting in part" to easily identify which parts they join with the majority, and which sections they do not.
Federal judiciary of the United States The federal courts are composed of three levels of courts. The Supreme Court of the United States is the court of last resort. It is generally an appellate court that operates under discretionary review, which means that the Court can choose which cases to hear, by granting writs of certiorari. There is therefore generally no basic right of appeal that extends automatically all the way to the Supreme Court. In a few situations (like lawsuits between state governments or some cases between the federal government and a state) it sits as a court of original jurisdiction.