I think you are referring to AudienceStore and EventStore, since they generate JSON files as their output.
They are explained here
More on AudienceStore setup
More on Event Feed setup
Basically, the difference is that EventStore can store a record of an incoming event as soon as it received by Server Side CDH. AudienceStream is not relevant to EventStore - it operates on the "raw" event data before it is processed by AudienceStream, if AudienceStream is enabled (it need not be).
AudienceStore, on the other hand, is actually a specific AudienceStream connector. So
a. You are dealing here with Visitor and Visit attributes that are stored, not Event attributes.
b. Just like any other connector, you configure AudienceStream to tell it when exactly you wish to write the record to AudienceStore.
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