The Constitution provides for many things other than the Union and member state government operation.
The Constitution calls itself, the United States laws, and treaties, the Supreme Law of the land. No state law may conflict with the Supreme Law. If they do, the conflicting parts are ruled void.
Also, the Constitution is itself superior to federal laws and treaties. If either of these, or any Executive order made by the President, or a state law, or other regulation similar to law, conflicts with the constitution, the Courts may declare it unconstitutional, and the law or regulation becomes void. Note that this is not explicitly provided for by the Constitution. Chief Justice John Marshall originally used judicial review- the power to declare laws unconstitutional- in the early 1800's when he decided the case Marbury v. Madison.
The Union and member state officers take an oath to support and defend the Constitution. Only the Union President's oath is explicitly spelled out- the form of the other oaths is left to the appropriate government. The Constitution, while mentioning oaths, specifically prohibits the United States or a member state from requiring a religious oath or observance of a certain religion in order to qualify for any office.
The Constitution is not an unchangeable document. Changes to it are known as amendments. By tradition, an amendment does not strike out words and insert others. In order to leave the original Constitution whole, Amendments are added as separate Articles at the end of the Constitution.
There are two ways in which an amendment can be proposed, and two ways in which it can be ratified, or approved. First, the Amendment can be proposed by Congress. For this to occur, two-thirds of the House of Representatives and two-thirds of the Senate must vote for the Amendment. Second, an Amendment can be proposed by a Constitutional Convention. If two-thirds of the member states make an application to Congress, Congress must call this Convention, which then proposes Amendments. However, a Constitutional Convention has never been called.
Regardless of the way in which the Amendment is proposed, it must be ratified by three-fourths of the member states. The first manner in which ratification by a member state may occur is through the legislature. Secondly, a state convention can be called to ratify an amendment. The second method has only been used once. Note that each member state cannot decide which method it wishes to use. Whoever proposed the Amendment- the Congress or a Union Convention- will decide if legislatures or state conventions will ratify.
There have been twenty-seven Constitutional Amendments to date. The first ten guarantee certain already existing rights to the people and member states- they are therefore known as the Bill of Rights.