Here's the how-to. There are a lot of pictures... but really it's very easy. Once you make one, you can make them over and over again with different bags or pieces of paper.
First, start out with one of the large size bags and fold it in half lengthwise.
Now fold your bag in half in the other direction.
Fold the bag in half one more time in the same direction as the last fold.
Spread your bag out flat. You should have 8 little rectangles.
Cut through all layers of the bag on the center fold line as shown below. You won't cut into either of the end sections on the bag.
Refold the bag along the lengthwise fold and pop both cut sections out. Pinch the folds into place.
Squish the book pages together....
... and fold into a book shape. I usually fiddle with the pages at this point to see which ones want to fall where. Whichever page looks the best can be the front. All the pages will not necessarily line up perfectly... some may extend a little more than others, etc., but that's okay
When I made my minibook, I cut 4.5 x 6 pieces of black cardstock for each page. then I added my pictures, Teresa Collin's Giving Thanks paper bits and Basic Grey buttons. Each page got a title with pretty Dear Lizzy foam stickers. Starting with a base for each and adhering them at the end is a lot easier and hides the fact that there is a little variation from page to page in the book.
Since I was using black cardstock for each page, I inked the photo's edges with black Staz-On ink to match.
One or more of your pages will have a spot for a "pocket" depending on which way you folded your bag. You can use the pockets or glue them shut to make the book more sturdy. I made a little 4.5 x 6 card to slide into the pocket on the right (with the orange paper and black ribbon). This holds an extra photo that was landscape and I just didn't want to trim. The space on the back of the photo is for my journaling about the day.
Here is the last page... you can see the notch of cut for the ribbon to pop through on the right edge.