How does an amendment work?

Well you have some previously existing text with a specific meaning and you want to change the text or indeed change the meaning so you make an alteration. This is an amendment.

Examples:

"Henry made an amendment to his will to leave more money to his favourite charity".

"An amendment is created by Congress (The US House of Representatives and Senate). A 2/3 majority has to okay the creation of an amendment. In Total, there are 27 amendments to the US Constitution".