REST
A simple REST API with all CRUD operations. There is no authentication required for making those calls.
You can access the Swagger UI here
SOAP
A simple SOAP API with a couple of simple methods. There is no authentication required for making those calls.
You can access the WSDL at here
SQL
A standard MS SQL server with access to the Customers table in the database. You need a connection string for making connections to the database and it is already available in your FRENDS instance as an environment variable named FrendsExampleCRM.SqlConnectionString