In order to get you started on an essay on the Reliquary Shrine, I would suggest to firstly start of with an explanation of what a reliquary is. You could mention that a reliquary is a shrine which was used to keep relics safe. You could even include a definition of relics. For example, according to the Encyclopedia Britannica, relics are defined as "objects of worship or veneration, generally consist[ing] of all or part of the skeleton (such as the skull, hand, finger, foot, or tooth), a piece or lock of hair, a fingernail, or garments or fragments of clothing." As these relics were used for worship, it was only right that they would have had to be stored in a suitable container. A reliquary therefore needed to be designed in a way that appropriately reflected the importance of the person who's mortal remains were stored inside.
Following on from this, I would then suggest you explain that the Reliquary Shrine is generally attributed to a French goldsmith, Jean de Touyl, and that it can be seen in The Cloisters, which is a branch of the Metropolitan Museum of Art in New York.
You might then want to continue to write in more detail about the Reliquary Shrine and describe what it looks like. You could, for example, mention that the Virgin Mary and Jesus as a child form the centerpiece of the Reliquary Shrine. You could then continue to describe the shrine in even more detail—for example, by describing the expressions on the faces of Mary and Jesus, or by mentioning the angels, which also form part of the shrine's decoration.
Following on from this, you could explain the various materials used in building this shrine, such as gilded silver and translucent enamel.