On the Laravel News site today they've posted a tutorial helping you learn more about the grant types in the OAuth2 functionality provided by Laravel Passport.
OAuth2 is a security framework that controls access to protected areas of an application, and it’s mainly used to control how different clients consume an API ensuring they have the proper permissions to access the requested resources.
Laravel Passport is a full OAuth2 server implementation; it was built to make it easy to apply authentication over an API for laravel-based web applications.
For those not familiar with some of the terms around OAuth and its handling, they start with a few brief definitions (those that are familiar can skip them). Following this the post gets into the creation of a two kinds of grant handling with Passport: third-party authorizations and first-party applications (your own apps authenticating against the OAuth server). The post ends with a brief mention of creating access tokens manually, but points out that thing functionality should probably only be used during testing.