Primary sources are the actual laws and rules issued by governing bodies that tell us what we can and cannot do. The four primary sources are constitutions, statutes, cases, and regulations. These laws and rules are issued by official bodies from the three branches of government.
Every state in the U.S. and the nation as a whole has a Constitution. A constitution is a fundamental set of principles around which all other law is derived and organized. The United States Constitution is the supreme law of the land and the source of all government powers. The Mississippi Constitution is structured similarly to the U.S. Constitution but it only governs the state.
Constitutions are created at constitutional conventions. Delegates to these conventions work together to create a new constitution, which is then approved by the public. The U.S. Constitution was created at a convention in 1787; there has never been another U.S. constitutional convention held, but it is allowed by law. Though an entirely new constitution can only be formed from a constitutional convention, the constitution can be amended at any time. It is much more difficult to amend the U.S. Constitution, because in addition to requiring approval by 2/3 of both houses of Congress, it also requires ratification by 3/4 of the states. Even so, the U.S. Constitution has been amended 27 times - the first 10 amendments happened at the same time and are called the "Bill of Rights."
The Constitution of the United States and the Declaration of Independence by 
Statutes are the formal written law passed by a legislative body. Before a law is enacted, it begins as a bill in the legislature. Both the United States Congress and the Mississippi state legislature pass statutes.
A bill can begin in either house of the legislature, but must pass both to become law. It also must be approved or rejected by the executive (the U.S. President for federal laws and the state governor for state laws). A rejection is called a veto. To approve the law, the executive must sign it. However, if he or she does not sign it, it is not rejected. After 10 days have passed, if the executive has not vetoed the law, it becomes law without his or her signature. If the executive vetoes the law, it is not doomed. The executive must return the law to the legislature with his or her reasons for objecting to it. If the law passes both houses again with a 2/3 approval in each, it becomes law despite the veto.
A case is a dispute between two or more parties that is resolved by a court. The parties can be individual people or groups of people, the government, or incorporated entities. Cases can be either civil or criminal and are brought in both state and federal courts, but only the government can initiate a criminal case. Cases begin at the trial court level (also called the district court). If one of the parties disagrees with the decision, the party can appeal its case. Appellate courts, and sometimes trial courts, issue written decisions, which are often available online for free.
One of the roles of the courts is to interpret and apply statutes and constitutions. A court can also strike down statutes it believes to be unconstitutional. Sometimes, the legislative body may take the opinion of the court and use it to help re-work a new statute that will "pass constitutional muster." Additionally, if a court says a law is too vague to be applied in a particular case, the legislative body may go back and re-write the law to make it more specific. There is a back-and-forth to the process, but in the end, it is all part of our system of "checks and balances."
Regulations, also called "administrative law," are sometimes confused with statutes but they are very different. Regulations are issued by administrative agencies, which are part of the executive branch of government. That means that regulations are not decided by people who are elected by the public, but rather, people who are appointed by the president or governor. But there are rules that require regulations to go through a public notice-and-comment period before they become final. Regulations are issued pursuant to a statutory authority, that is, a statute was passed that directed an administrative agency to develop regulations that will elaborate upon the statute. But regulations are very useful because they often get down to the nitty-gritty details of carrying out the directives laid out in statutes. Regulations are primary law but they are not equal in weight to statutes or cases. A statute can override a regulation or a court may decide that an agency didn't have the authority to pass a regulation.