How does Couchbase _count?

Does it just have unique index entries and increase by one when I add a new document entry?
does it always create a new index entry and actually count them whenever I trigger the View?

My understanding based on your question is that you are talking about the _count reduce function that Couchbase provides for views. So let me answer with this in mind.
So when you are creating a view, Couchbase create an index and this index is updated based on the various operations on the document. This is what we call “incremental map reduce”. You can find more information about index and views where:
So the count is based on the index that is stored on the disk and calculated based on the parameters/groups you send to the view when doing a query.
Let me know if you need more information.