As written in the Core Rules: Bards use magical performances to alter the odds in favor of your allies. You confidently alternate between attacks, healing, and helpful spells as needed. This remains true in Khallah Vex, though with some notable differences in focus and intent.
In the Viridian region, there are several clear traditions.
The Civic Collegium of Axiandros in Tamiriya may be the oldest facility of its kind in the world; it certainly claims to be, and given the longevity of the Empire and the city, it could easily be true. Prospective Bards, actors, and all manner of performers from across the known world come to learn and train here.
The Royal College of Record & Recitation is the smaller and newer equivalent based in Assetallis. Bards and other performers train there, but it is more than just the performing school. Scribes, historians, tax collectors, heralds -- all manner of related professions and skills are taught at the increasingly popular school.
Of course, it is still possible to be self-taught, have a mentor, or otherwise base a Bard in a background that doesn't include official training.
If a player wishes to have their Muse identified, conversation with the GM is needed. Some of the listed options such as various Golarion deities, dragons, and others are absent in Khallah Vex (though others exists).