Web API - How to access a API using a token

I am new and learning web apis

This is a sample API that provides access to a books database.

There are 2 sample API operations available for 2 databases, say ABC and XYZ

/api/{abc or xyz}/books: This returns the books that are available /api/{abc or xyz}/book/{ID}: This returns the details of a single book To access this API you'll require an API token.

Also just like any realworld API these may be flakey at times

I want to Build a web app to allow customers to get the cheapest price for books from these two providers in C#.

The API token provided to you should not be exposed to the public.

Any help would be appreciated. Thanks in advance.