Who sells voyages in Sea of Thieves?

Could you please elaborate on who is responsible for selling voyages in the popular game Sea of Thieves? Are these voyages offered by the game's developers, or are they sold by NPCs within the game? Additionally, how does one acquire these voyages, and what kind of rewards or objectives do they typically entail? Is there a limit to the number of voyages that can be undertaken, or can players embark on as many as they wish?