The author is a user role in WordPress. The author can access the backend of the website But does not have complete access to the website.

The author can Upload files, write all files, edit files, publish and delete his files. The author can edit his name and password also.
Author user role is not very useful in developing websites because it allows users to delete posts from the website backend. If you have hired an author for your website then he might delete his work if you fire him. It is required to understand the user roles and create custom roles as per requirements.
Authors can create their author’s bio page with help of the author’s archives page. It shows the list of blogs created by that author. It is also possible to add a list of authors with their photos on the sidebar.
WordPress allows authors to share their bio and details such as name, date of birth, location, social profiles, and more.
How to assign user as author?
To crate a author you can assign existing user as author or create a new user and assign him as a author.
Simple you can create author from Users Tab.
To add new user click on Add new user and create a role of author. And to create existing user an author, Find that user from existing users and assign him as author.
How to Remove Author?
Sign into website as admin and change the use role of the user or delete the user.