Use of strtok in C: How do I use them correctly?

Question

Hi guys.

While solving some code coaches, I found out that strtok function from string.h library is pretty useful. However, I'm not sure how to use that.
Is the thing like strtok divides the given string into two parts? And that is the reason why we use them in loops? Even so, how does it divide NULL there?😶
noise = strtok(NULL, " "); [plz check the code.!]
https://code.sololearn.com/cckfSzsNfKui/?ref=app