There are a few different ways to make POD books:
1) If you're already on Amazon, they make it very easy to create a paperback (I think they now have a button that says "Make a paperback" or something like that.) Even if you don't want to do that, they provide templates for the interior as well as book cover (you'll have to upload a spine and back, but they provide a template for the size). I did my first books this way.
Big warning: author copies will come with a strip in the middle of the book cover saying "NOT FOR RESALE." If you want copies for book signing (when those happen again), you'll want to order them at full price (not author copies)
2) B&N has a program where you can upload your book for POD either as a private book or for sale. I use the private (personal) option for books I make for a local Sherlock group that puts out.a book for their own members and not for sale. Same printer, etc, but no need to have an ISBN. If you don't want to list these at B&N for sale, they are cheaper than any of the other PODs I could find (Lulu, etc.)
If you want to sell on B&N, you can do that too. They will supply an ISBN, if you want, but then it is listed as published by B&N.
3) IngramSpark will produce and distribute your books to bigger platform (Draft2Digital will too, but I'm not familiar with them)--unless you tell them (there's an exclusion you can check for Amazon and Apple), they will go to Amazon, Apple, B&N, Kobo, etc. both eBook and paperback. The drawback: they require an ISBN and it will be on sale (why I like B&N for the personal/private option). They have a really archaic book cover program and I use a professional to help me with getting it right for the paperbacks (I don't have the right software and prefer to us my book cover designer to do it than to pull out my hair). There's a charge for uploading, but they have a discount code that drops it to $0: FREE2020. Sign up for the blog and you'll find out what the new code is).
Any more questions, please ask.