This challenge revolves around the texture analyses from lesson 2. The only difference is that we are doing 25 rows rather than just one page's worth.
This is actually where the exercise began, as an independent challenge. I ultimately figured it was valuable enough to incorporate it into the main lessons themselves.
While you can watch the video linked here, I do recommend that you go to the texture analysis page and read through it thoroughly. In addition to this, do not plan to complete this challenge in one go. I strongly encourage you to do it in parallel with the other drawabox lessons, completing it one row at a time.
The reason for this is that it will give you the opportunity to process what you're learning and internalize your own discoveries. These aren't things the brain does quickly - it often requires long periods of time away from the task in question in order for the concepts to properly sink in. Grinding away at it simply won't give you that.