Main Database : Type information to connect to the database.
DSN ( Data Source Name) : Data Source name in the ODBC settings.
File DSN : File source name in the ODBC.
Creating a File Source Name allows you to centralize and share them in order to be accessible from workstations. You won't have to create an ODBC for every workstation.
User : SYSADM.
Password : SYSADM.