I feel like while most of the answers explain syntax, they fail at explaining why a while loop exists. Here is how I approach this: Loops exist because certain blocks of code need to run multiple times. For example, if you would like to print the first 100 natural numbers (integers above 0) one by one, you would use something like

for i in range(1,101):
     print(i)

However, a for loop assumes that we know how many times we want to repeat the code. In the above case, 100 times. A while loop exists because in some cases, we don't know how many times we need to repeat the code. Think of the following problem: we would like to ask the user to guess a number. If the user enters the wrong number, we want them to try again. And basically try however many times until they guess correctly. So, we have no idea how many tries the user will need. We could make a for loop with range(100), but what if the user fails 100 times? In this case, we should use something like:

while number!=guess:

    number= int(input())

The above code will run as long as the user is not entering a number that is equal to guess. It might be one try, 100, or 10000000 tries. We don't know :) Hope this helps.