To purchase

This way:

1. Click the "Create a New List" button just above this panel.
2. Add as many books as you wish using the built-in search on the list edit page.

Or that way:

1. Go to any book page.
2. In the right-hand column, click on "Add to List." A drop-down menu will appear.
3. From the drop-down menu, either add your book to a list you have already created or create a new list.
4. View and edit your lists anytime on your profile page.