This is what I mean. AS the name implies, it is the settings that allow your application to connect to the SQL server. So you have 500 gas stations and one sql server located at the main office. In order for these 500 office locations' application, if installed at each gas station location, will require connection string, or connection detail, shown below, in order to read and write data. for this data stream to travel to the central office, you need some sort of connection, be it internet, dial up, satellite etc.
https://www.connectionstrings.com/sql-server/
Driver={SQL Server};Server=myServerAddress;Database=myDataBase;Uid=myUsername;
Pwd=myPassword;