what is swagger used for code example

Example 1: what is swagger ui

The Swagger UI is an open source project to visually render documentation for 
an API defined with the OpenAPI (Swagger) Specification

Example 2: what is swagger

Swagger is an open-source software framework backed by a large
ecosystem of tools that helps developers design, build, document,
and consume RESTful Web services.
Swagger allows you to describe the structure of your APIs so that
machines can read them.
The ability of APIs to describe their own structure is the root of
all awesomeness in Swagger
similar to xml schema but for Json

Do you have API documentation website for your API?
Yes, we use swagger for our api documentation, and this is where
the description and guidelines of API endpoints are 

Where do you keep API reference documentation in
your Project?
We use SWAGGER to keep API endpoints and descriptions. I
normally go there and learn about API methods and how they
work.