Question

Where do I find the first assignment?

Answer 1

Find assignment 0 (the first assignment) here:
http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-00sc-introduction-to-computer-science-and-programming-spring-2011/unit-1/lecture-2-core-elements-of-a-program/

It's at the bottom of the page.

Answer 2

Each assignment seems to be at the bottom of the page of the lecture it's due for rather than the lecture it's assigned in.