Help to a test

Hello, I really need your help. I'm a person that doesn't know anything about coding, but I study IT. I will be going to a test tomorrow about all we learned in class. I will be getting 3 questions, 1 about OS, 1 about network, and 1 about programming. The teacher said it will be very easy, like I need to know why the code is failing. Like this code: x=[1,3,5]; y=x[1:3]. I don't know by myself if this code is correct or not, but you know. My question is, do people have a website where you can write the code and it corrects it for you and explains it for you?