This object is used to store post objects that are stored in the database and to get back you will use the get_post function.
Inside the object there is post_tye, post_title, post_date, post_content, and many more things that can be grabbed from the database.
The role is to collect the objects that are stored in the database. Then when you use a function to get something then it will be ready to use.
WP_Post is used to collect data about your content from the database and then you can use that to display information when you want by using any of the functions to call the object.