The for loop is used when looping over a sequence, such as a list, tuple, or a collection of objects. Let's start with a simple example and expand on the concept to see what the Python syntax allows us to do:

# simple.for.py
for number in [0, 1, 2, 3, 4]: 
    print(number) 

This simple snippet of code, when executed, prints all numbers from 0 to 4. The for loop is fed the list [0, 1, 2, 3, 4] and at each iteration, number is given a value from the sequence (which is iterated sequentially, in order), then the body of the loop is executed (the print line). The number value changes at every iteration, according to which value is coming next from the sequence. When the sequence is exhausted, the for loop terminates, and the execution of the code resumes normally with the code after the loop.