Do you have any idea how much work explaining code line by line is?
Every single line needs a paragraph of explanation! For example:
int next = r.Next();
Create a new variable called "next" which can hold a integer value. From the previously declared Random instance "r", call the "Next" method to get a new random number, and assign it to the "next" variable.
Can you imagine how long it would take us to explain even a very short code fragment like your example, line by line?
No. It is not going to happen. If you have a specific problem, then ask a question about it. But think first - would you want to sit down for 45 minutes and type up a line-by-line description for no good reason?
If the code you found somewhere doesn't do what you want, either ask the person you got it from, use the debugger to find out why, or write your own. We aren't here to provide random technical support fro every bit of code on the internet.