Welcome to the Community!
I do realize that some of the documents that I will point you to will be a bit out of date, compared to the most recent Distros, but more relevant to the Ubuntu MATE experience than generic books and, if nothing else, will prompt you to consider/research what I will have presented in those documents.
I invite you to have a look at some/all of the documents that I offered in my GitHub repository:
You could use those to create your own "Documentation" of your Desktop, if you like to have a written record ... what you did where ... for your specific box.
Hope that helps!