In the time before time and history, the Dawn War raged between the Gods and the Primordials. The two sides seemed evenly matched but the war was wrecking creation. Eventually, the Primals, the living spirits that represented the world itself, manifested themselves. They intervened in the war and through a series of demonstrations of their own powers and alliances, the Primals ended the war. Although the Gods are generally considered the winners after the war, both Deities and Primordials are banished from the natural world.
Originally, Primals were exclusively nature spirits. They took the forms of forests, oceans, lakes, rivers, deserts, mountains, etc; however, as Primals are a representation, it didn't take too long for Primals beginning to manifest as concepts and places from civilization. Primal spirits from libraries as a book, or primal spirits who have attached themselves to a royal palace for example.
Druids, Shamans, and Seekers are how most mortals are able to communicate with spirits.