how to understand codes

[YCL105]

Hello, I'm a beginner. I have a few superficial questions to ask you. My code foundation is poor. It's convenient for me to learn code by asking a few small questions. Please forgive me if you feel uncomfortable. What are the labels of the three structures and how to calculate the loss respectively. What are the concepts of SR factor 2, 3 and 4 and kenel width mentioned in the paper? Thank you again.