Some apps allow you to import and export files from the app using iTunes or a third party app like iFunbox.
The types of files are specific to each app and may be, for example, recorded audio files, app presets, or wavetables.
For some apps, this may be the only way to import/export some types of files (e.g. Animoog timbre files).
Some apps do not have iTunes file sharing functionality.
Some apps have iTunes file sharing and alternative methods of importing/exporting files such as using the Files app, copy/paste, open in, AirDrop, and wi-fi file sharing. Some apps may have all of these methods (e.g. AudioShare).