The range() function in Python generates a sequence of numbers. When you write range(3), it creates a sequence that starts at 0 and goes up to, but does not include, 3. This sequence will be [0, 1, 2].

The for loop then takes each number from this sequence, one by one, and does something with it. In this case, it prints the number. So the loop with for i in range(3): tells Python to start with the first number in the sequence 0, then go to the next number 1, and finally 2, printing each one.

Here's what happens step by step:

The loop starts, and i is set to the first number in the range, which is 0.
The print(i) command is executed, and 0 is printed.
The loop goes back to the start, i is set to the next number in the range, which is 1.
print(i) is executed again, and 1 is printed.
The loop goes back to the start one more time, i is set to 2.
print(i) prints 2.
Now, there are no more numbers in the sequence generated by range(3), so the loop stops.