Switch Access Training With Music plays audio files that you select with the Media Picker. That interface pops up first thing whenever you open the app. While those files could contain songs, sound effects, conversations, or othr types of audio, we will tend to refer to them here as "songs."
You cannot play audio with this app by "streaming" it from Home Sharing or the Cloud, so you will need to select from files that are already stored on the device; in other words, if you want to play those sorts of remote files, then download them to the device first.
In the standard Music app you can create playlists that will appear in the Media Picker, then all you have to do is select a playlist when you start (rather than a set of individual songs). This can be much more efficient than repeatedly creating the same playlist for a particular student, classroom activity, or similar familiar context. You can also mix-and-match multiple playlists, albums, songs, and so on.
After you select one or more files, the app sets up a queue. Each file is played in turn as a sequence of timed clips, advancing clipwise every time you hit a switch. The trainee just keeps hitting the switch until they run through the playlist (which will then repeat). You can add more songs anywhere along the line.
As for the switch, it can be:
The other Information pages explain how you can adjust such features as:
Mostly, just mess around with the app until you feel comfy.
By the way, while you can set a preference for shuffling the list (or not) in Settings, when you run the app for the first time it will adopt the existing Shuffle setting for the device. The first time that you use the app, then, the first song that gets listed in the queue might not be the one that was at the top of your chosen playlist. If that is an issue, you can turn Shuffle off in the Music app before running the app the first time.
NOTE WELL: This app is set up as a "system" music player (rather than an "application" player). The advantage is that you do not have to select a new playlist every time you come back to the app (such as if you leave temporarily to change some Settings, or go to use a different app for a while, which includes a trainee leaving the app). While the potential disadvantage is that the music will continue to play if you leave or close the app, that is easy stop just by: (a) returning to the app and pausing or stopping, or (b) exposing the system's audio controls (i.e., swipe up from the bottom of the screen).