Most often in America (and common law countries) you will need to find case law
Unless you are looking for a specific case (i.e. Brown v. Board) or statute (i.e. 14th Amendment), reading Law Review articles can provide a more comprehensive understanding of a topic (i.e. segregation).
In America, courts create laws by interpreting prior cases and statutes (laws passed by legislative bodies). Case law comes from the courts, ranging from state lower courts all the way up to the U.S. Supreme Court. Case Law can be found both in HeinOnline and by using the Case Law search facet in Google Scholar.
Statutes are laws passed by legislative bodies such as the U.S. Congress or a state's legislative branch. Statutes are often compiled into code books.
Beginning in Law School, legal scholars and lawyers will publish articles on topics in Law Reviews. These journals will often explore the legal context of the topic by citing relevant legal decisions and statutes.
Prestigious Law Reviews often correlate to the top ranked law schools or State Bars. Law schools often publish multiple Law Reviews, many are specialized, focusing on a specific topic in the law. Law review articles can be found in the HeinOnline database.