A connection is just that, a connection to the database.
A query is a query.
DIg into the docs and study the examples under database and eloquent.
https://laravel.com/docs/5.7/database#using-multiple-database-connections
https://laravel.com/docs/5.7/queries
https://laravel.com/docs/5.7/pagination
https://laravel.com/docs/5.7/eloquent
https://laravel.com/docs/5.7/eloquent-relationships
And more
Jeffrey has many free intro videos.