I got into bookbinding roughly 6 years ago and this DeviantArt thread was the first source I used.
It is categorized in two main groups: Adhesive bookbinding methods, and non-adhesive bookbinding methods.
You will find in each group images and maybe a simple explanation of different methods for bookbinding alongside links to tutorials and guides elsewhere online, some of them video guides and others are blogposts.
One of the links to some of the methods led me to discover a youtube channel by Sea Lemon, who, among other things, has a lot of good guides on different techniques for bookbinding.
And from her channel I came to learn about the existence of a multi volume text book series called Non-adhesive Binding by Keith Smith, of which I only tried the first two volumes but I ended up learning a lot of the technical jargon and terminology used in bookbinding.
Now, a lot of people bind their own journals or sketchbooks, but if you wanted to bind actual books you get online, you'd need certain software that will help you organize the pages into booklet format and format them into proper sections for printing.
A couple of the tools that I used are:
There are others obviously but I've been happy with these two.
As for sources for books, you can find a lot of public domain books in places like Project Gutenberg, and The Anarchist Library, or you can find them through official publishers that offer open access publishing (which, in certain academic circles is becoming more and more popularized).
