The jamstik+ does not come with builtin sounds. The device outputs MIDI format note codes and the receiving device & software (such as the jamstik+ app & GarageBand) translates these codes into sounds. To get started with your jamstik+, please read the Getting Started Overview.
In addition to standard guitar sounds, there is a large variety of other sounds available in many MIDI based apps and Software. Check out Apps That Are Compatible With The Jamstik+