Answer:
It basically means that Romeo when first seeing Juliet thought she is so beautiful that her beauty is brighter then a torch
Step-by-step explanation:
This quote is from this line when Romeo first sees Juliet, before he knows who she is. Basically, with that line that Romeo is saying that Juliet is so beautiful that her beauty is brighter than a torch. She is so bright, that the torches learn to be bright from her. It is another metaphor on Juliet's beauty.