Hi, what is this? genuine question?

Hello! So a month or so ago my aunt's step daughter came back from mexico and brought me this as a gift. I know its for protection and that its a necklace of sorts, and im pretty sure thats the virgin mary and jesus. But thats all i know. And i feel bad that its just sitting in my room with no knowledge of what it is. I would also like to know how your suppose to where it, and if there is preferred time when your suppose to wear it