There are two main methods that can be used to add amendments to the United States Constitution:
Proposal by Congress: An amendment can be proposed by a two-thirds majority vote in both the House of Representatives and the Senate. Once proposed, the amendment must be ratified by three-fourths of the states (38 out of 50) either through their state legislatures or through state conventions.
Proposal by Constitutional Convention: An amendment can also be proposed by a constitutional convention called for by two-thirds of the state legislatures (currently 34 out of 50). Once proposed, the amendment must still be ratified by three-fourths of the states (38 out of 50) either through their state legislatures or through state conventions.
These are the methods outlined in Article V of the U.S. Constitution for adding amendments, and they reflect the process of formal amendment as outlined in the Constitution.