Let's say you had a list of full names, where the name would consist of a title, followed by first, middle and last name, or maybe just title and last name. You can sort this list by last name only, by creating a temporary list of sublists of type [last name, full name].
Python makes all of this relatively easy. The last name element is obtained by splitting the full name into a list and using the last element of that list. When the temporary list of sublists is sorted, it is sorted by the first element in the sublist. Once the sort is done, simply recreate a list of the sublists' second element, removing the temporary last name item. I hope, I added enough comments in the code, so you can follow the logic.