Talk about agile development as I understand it

"Agile development" https://www.ciandt.com.cn/ has almost become a popular topic on the Internet. Everyone is talking about Agile, Scrum, XP.
My understanding of "agile" is still in an exploratory stage. There are a lot of information on the Internet, all kinds, and there will be a lot of barriers for beginners. I just took this opportunity to write an article to help me sort out and summarize my knowledge. On the other hand, I hope it will be helpful to those who are new to it.
How much do you know about "agile development"?
Agile development is a human-centered, iterative and step-by-step development method.
It is not a technology, but a development method, that is, a software development process. It will guide us to complete the development of the project step by step with the prescribed links. Because it uses iterative development, the main driving core of this development method is people.
Then why do you say that talent is the main driving core? We have learned the waterfall development model, which is driven by documents. Developers develop according to the requirements documents provided by the product department. The core of everything is the document, so the document is the A core in this model. The significance of agile development is that it only pays attention to the important points in the document, or to simplify the document as much as possible. In fact, agile development pays more attention to the communication and exchange between people. So it emphasizes people as the core.