The key points are - Congress may propose amendments - if two thirds of each House agree; or two thirds of the state legislatures call a Convention for the purpose of amendment. (This last procedure has never been used)
Any such amendments proposed must be ratified by the legislatures of three-fourths of the States (38 states at present)
Twenty Seven Amendments have been passed. The first ten are referred to collectively as "the Bill of Rights". The 18th Amendment introducing prohibition was repealed by the 21st Amendment. An article on "failed amendments" can be accessed here.
