Homework 0 is essentially a warm-up to make sure you've installed playcrypt, know how to retrieve and submit homeworks, and have read the syllabus.
There are two files you'll want to look at / download: a PDF describing the homework in text or mathematical notation, and a python file which you should edit the indicated functions of.
Submit on gradescope. There are two gradescope assignments: "Homework 0, Part 1" and "Homework 0, Part 2" — be sure to submit both!