When uploading your book, you will be given an option of adding bleed or no bleed. Here is some information on the KDP site itself with an explanation.
The page margins you choose will depend on the number of pages you want in your book, for the most part. For example, uploading a basic notebook will probably not require you to stipulate margins as the lines of the book will go from one side of the page to the other. You would select the ‘bleed’ option for a notebook for this reason. You don’t need to select ‘bleed’ if your content will be contained within the margins of the pages, but if you have even one element, such as an image, that spans across the entire width of the page, then you need to select the ‘bleed’ option. You can still set margins for the rest of the content.
The Amazon link above will tell you how to set your margins depending on the size of the book.