mjes - there are three "sticky" Bookmarks at the top of the Bookmark options - "I want to cook this", "I've cooked this" and "Favorite recipes". By clicking "I want to cook this" an orange chef's hat appears before the recipe title and applying "I've cooked this" puts a green hat in front of the title. This is the Help section on Bookmarking a recipe and you can also follow Tutorial 4 in the tutorials accessed from the green Need Help? button at bottom right (not available on phones).
To apply the Bookmarks to the recipes listed in Notes, the recipe does need to be on your Bookshelf. If it is, click the recipe title and you can apply the Bookmark in My Bookmarks in the right column. Don't forget you can also view Notes on your Bookshelf tab, where every recipe listed is already on your Bookshelf.