I've linked in the materials from class today (the quiz, answers, and code from my on-screen examples (points and elephants and snakes, oh my!).
I will point out that Chapter 6 of HtDP is a good source for information on structures in PLT Scheme. I will not be explicitly "assigning" this material for you to read. That said, it is very readable, and I recommend it as a resource if you want to augment my examples from class.
Section 6.3, in particular, talks about data definitions, and provides a number of exercises you could work through. We'll be doing some of these kinds of problems in lab, so no hurry... but I want you to realize that the resource is there.