How do I get addresses that already exist in another system (for instance in my school’s management system) ?

You can import addresses from another system, such as FileMaker Pro™, Excel™, Access™...

You must first export the addresses from that system (text format, separator between fields : tabulator, separator between records : return). Then import them in BiblioMaker (use the Simple import format). The import format (fields order...) is described in the handbook.