The Storefront API is the foundational layer of custom storefronts. It provides you the commerce primitives to build custom, scalable, and performant shopping experiences

The Storefront API provides access to Shopify's primitives and capabilities such as displaying products and collections, adding items to the cart, calculating contextual pricing, and more.

You can use the Storefront API to build unique commerce experiences on any platform, including the web, native apps, games, and social media, using the frontend tools of your choice.

Authentication and Authorization :-

Public Authentication: The public token is used for client side queries and mutations. As every buyer has a different IP, the token scales to support large amounts of traffic.

Private Access: The private token provides authenticated access to the Storefront API and is used for server-side queries and mutations.

!!Caution!! :-

Unlike public access tokens, private access tokens should be treated as secret and not used on the client-side. We recommend only requesting the scopes that your app needs, to reduce the security risk if the token leaks.

Learn more about authentication.

What is the Headless channel? 

Make headless and self-hosted Hydrogen experiences possible in the Headless channel without needing to create a custom app.

The Headless channel provides a single place to create and manage access tokens for the Storefront API. You can use the channel to create multiple custom storefronts. Storefronts that you create through the channel automatically include public and private access tokens with shop permission for the Storefront API. In the channel, you can rotate your private access token and manage storefront permissions.

Additionally, the channel gives you all of Shopify's channel features, such as product publishing and order attribution, and analytics and reporting sales by channel. Order attribution is at the channel level, not the storefront level.

Refer More more :-

 Get started with the Headless channel.