I don’t get double linked lists — Day 4

I did my Hacker Rank day 2 /100 challenge and got so frustrated because the code that I had executed on my terminal but for some reason, I kept getting errors on Hacker rank’s compiler. So I still have to figure that out. And then I had my object-oriented programming lab which had to do with doing different methods to linkedlist and I honestly still don’t get it but I will keep chugging on it.