About bulk loader

hello~
First of all, thank you for answering my question~
I try this.But maybe I don’t really understand how it’s used, so I have a few questions.
In my understanding, the bulk loader method to import data in batches is to import into the dgraph cluster by instruction under the premise that the dgraph zero service is turned on.
But that doesn’t seem to be the case.
And in this method,where does my data source come in?