This app datasource helps you access data from other apps or just group your information by content-types (like tables).
You can use it from the visual query designer or from code. Here is an example in the query designer:
The most common use cases are:
Accessing "Tables" of the current app
Just add the App data source, create new connections and name the Out according to the content types as you need them. This is best seen in the large image on the left-most data source.
So if you have a blog-app and need a few streams like
Then just pull out one each and name them accordingly.
Accessing some or all data of another app
Note that this can be done in code since 2sxc 7, but needs 2sxc 8.5 to do this in the visual query designer.
In this case you can do the same as above, but make sure you configure the data source with AppId and optionally the ZoneId.
To set these values in C# code, the properties of ToSic.Eav.DataSources.App class are