Learning the business of writing is an important part of being a successful writer. Understanding copyright, fair use, and other laws governing intellectual property is essential. You don't want to face a lawsuit, or have your books banned by Amazon or another publisher because you stepped over a legal line. Ignorance is no excuse.
Disclaimer: This is only a brief overview of the writing business and is not meant to be either comprehensive, or taken as legal advice. Find a competent attorney with experience in Intellectual Property Law to answer your legal questions.
Your first paragraph ...