How to work with mailchimp API?

Question

PHP

Good afternoon.
I read the documentation on mailchimp.com , but did not understand how to install the API. That is, I realized that I need to download composer via the command line on the server, but I don’t understand why you need to install something if these libraries should be .
I want to know exactly how my hand-written website works with the mailchimp API. Also, I don't want to litter the project directories with various installers.
Why do we need composer.json, why do we need to install this composer?
I would like to find a way to easily and transparently connect the mailchimp API. For example, throw a file with functions (using the analogy of connecting the jQuery library) and simply use it in your code (that is, without settings and entering commands on the command line).
PS: I have noticed that composer.json and a similar structure are used in some frameworks (eg YII 2), however I have not had to work with any framework.
PPS: also, if possible, throw off sources that will help you understand the topic.

Answer 1

Download from here https://bitbucket.org/mailchimp/mailchimp-api-php.
Take the src folder and include the Mailchimp.php file.
About composer, read a separate article habrahabr.ru/post/145946.

Answer 2

If possible, in more detail how to use it)
- view current lists
- create lists
- add users to lists