Authentication module will convert your application into multiuser platform where each user will get own account.
It's very important to say that you don't need to have a database where your users will be stored because we host that database for you. In control panel you only select which form fields you want to include during user registration. In most cases those fields will be: first and last name, address, city, ZIP, country, phone, fax, email and of course username and password. Also you will be allowed to define any amount of custom fields in registration form such as: gender, age ...etc.
Just like in other modules endpoints are diveded in private and public endpoints. Authentication module will create JSON web token which will protect your endpoints and make it private. When user is logged in endpoints should be private and protected by that token. For example if your application is web shop then each buyer should login into his panel where he will enter payment details and where he can buy products. For security reasons all endpoints after login should be private e.g. protected by token.