I think this week's challenge is pretty self-explanatory - this is just making us all aware of what we consume on a daily basis, plus getting in the habit of writing things down. When I did my previous challenge, I was surprised at how many bites or handfuls of this or that I actually ate all day long, being at home - and being accountable, even to a notebook on my counter that no one else would ever see, was good for me!
This can be as simple or as detailed as you like - For instance, if you want to list "Cheerios for breakfast, Taco Bell for lunch, snack, Casserole for dinner" that's great - but look how much more information you could learn about your habits and portion sizes if you wrote "3/4 cup Honey Nut Cheerios, 1/2 cup skim milk, 1 slice toast with 1 T butter, Chicken burrito with 2 T cheese and 1/2 cup refried beans, 12 potato chips, 1 cup noodles, 1/2 breast chicken, 3 T pasta sauce, ....." you get the picture.
If you want to make it more of a "journal" you can do that as well - why did you choose to eat what you did, did you stop eating when you were full, did you plan healthy meals ahead of time or find yourself scrambling for something crappy and fast because you didn't plan ahead? Did you find yourself eating "emotionally" at all? Were you thinking about calories or vegetable servings or fiber at all? One of my concerns is making sure I'm SITTING DOWN while I eat (uh, not in a drive thru)!
There are no hard and fast rules about this challenge, but like everything, you'll get as much out of it as you put into it! Good luck!