You have a three elements list.
The first element of your list is ele1
The second element is ele2
The third element is the list [subele1, subele2], so you have an element that is a list.
Python uses zero base index, that means that start to count from zero, so for the Python interpreter your elements are called in the follow way:
>>>my_list = ['element1', 'element2', ['subelement1', 'subelement2']]
The last print accesses to the first element of the third element, in zero base index that is the index 2-0
You can google Python Zero base index and you will have lot of information. That applies for all number indexed structures in Python, including strings and lists.