If the line notes that eNotes's version of this use are the same that your version uses, you are talking about the lines where Mercutio is talking about Tybalt and his fencing ability. (By the way, you can use that second box to put some of the lines in to be sure we're talking about the right ones -- if you ask further questions on here.)
What Mercutio is saying is that Tybalt is a really good fencer. He is saying that Tybalt does all his fencing moves just exactly how the instruction books would tell you to do them. And he says Tybalt is really good at killing people. So he is saying that Romeo is in trouble if they fight.