I just found this in the user manual. . . I'll give it a try.
The Files tab gives you access to files and folders throughout your computer's file system, as well as Studio One-specific content locations.
It is possible to import several file types from the Files tab into your Song or Project, including WAV (BWF and RF64), AIFF, REX, Apple Loops (CAF only in macOS), Ogg Vorbis, FLAC, and MP3 audio files, as well as Standard MIDI Files, and of course Studio One's Audio Loops and Music Loops.