You can noticed that in order to keep the water from staining the Windsor blocks, this group has decided to line the walls with clear plastic. The bottom is open to allow drainage and the plastic is 6 mils think so that it doesn't tear too easily.
Finally - you get to fill in the beds. For larger projects like this, use a good bulk soil/compost mix. Bagged product would be cost prohibitive. For just how to calculate how much soil is required to do this -                                   Click here