Basically this is tutorial which shows how to create a game with resource management and selling.So basically it teaches you to :
1.Use an event and mark it as a resource
2.Code to facilitate collection of the resource
3.A method to earn gold from the resource once you interact with a merchant
Hope this helps in your RPG Maker MZ projects
https://guidedone3gmailcom.itch.io/tutorial-to-create-resource-management-system