i dont understand what raise does to an exception. please someone can explain?

Answer 1

in your code you may want to control the variables' values or input etc. when you do that for a bad value with an if statement, you may want to raise an exception. that what does it mean: raising new exceptions.

Answer 2

Exception try to catch errors in your code. When you perform your Python code only 2 cases will be at the end: your code successfully running or your code raise exception and exit. :)